# rpoB ([RNA Polymerase](/knowledge/bioinformatics/rna-polymerase-structure-transcription-mechanisms) Beta Subunit): Rifampicin Binding Pocket and Tuberculosis Resistance Hotspots


## Key Takeaways

-   Mutations in the rifampicin resistance-determining region (RRDR) of the bacterial `rpoB` gene, encoding the RNA polymerase β subunit, are the primary cause of rifampicin resistance in *Mycobacterium tuberculosis* (Mtb).
-   The most frequent resistance-conferring mutations are S450L, H445Y/D, and D435V, which directly impair rifampicin binding to the RNA polymerase catalytic site, leading to reduced drug efficacy.
-   Rapid molecular diagnostic tests, such as Xpert MTB/RIF and line probe assays, target specific `rpoB` mutations within the RRDR to detect rifampicin resistance within hours, guiding immediate treatment adjustments.
-   The `rpoB` gene is essential for bacterial transcription and serves as a conserved phylogenetic marker for species identification in mycobacteria, including non-tuberculous mycobacteria (NTM).
-   Rifampicin, a cornerstone anti-tuberculosis drug, functions by inhibiting bacterial transcription through binding to the RpoB subunit, and its efficacy is directly compromised by these specific `rpoB` mutations.
-   The development of novel anti-TB drugs targeting alternative sites on RpoB or other essential bacterial transcription components is crucial to overcome resistance mediated by these prevalent `rpoB` mutations.

---

## Executive Summary & Key Metadata

The bacterial `rpoB` gene encodes the β subunit of the DNA-dependent [RNA polymerase](/knowledge/bioinformatics/rna-polymerase-structure-transcription-mechanisms) (RNAP), the core enzyme responsible for transcription in prokaryotes. As a central component of the RNAP catalytic machinery, RpoB contributes to the enzyme's catalytic center, DNA/RNA channel architecture, and the binding site for the first-line anti-tuberculosis (TB) drug rifampicin (RIF). Mutations in the rifampicin resistance-determining region (RRDR) of RpoB are the primary genetic determinant of rifampicin-resistant *Mycobacterium tuberculosis* (Mtb), a critical component of multidrug-resistant TB (MDR-TB). This manual provides a comprehensive, biophysically detailed reference for the gene, its protein product, structural biology, mutational landscape, and clinical significance.

| **Attribute** | **Details** |
| :--- | :--- |
| **HGNC Symbol** | rpoB (bacterial gene nomenclature; no human ortholog) |
| **UniProt Accession** | P0A8V2 (*Mycobacterium tuberculosis* RpoB) |
| **Representative PDB ID** | 5UAC (Mtb RNAP holoenzyme with rifampicin) |
| **Chromosomal Locus** | *M. tuberculosis* H37Rv: Rv0667 (position 759,807 to 763,325 on the circular chromosome) |
| **Primary Molecular Function** | DNA-dependent RNA polymerase activity; β subunit of the catalytic core; DNA binding; rifampicin binding |
| **Disease & Pathology Associations** | Rifampicin-resistant tuberculosis (RR-TB), multidrug-resistant tuberculosis (MDR-TB), extensively drug-resistant tuberculosis (XDR-TB) |

## 1. Genomic Locus, Chromosomal Organization & Isoforms

### 1.1 Genomic Context in *Mycobacterium tuberculosis*

In the reference strain *Mycobacterium tuberculosis* H37Rv, the `rpoB` gene is designated as Rv0667. It is located on the circular chromosome at coordinates 759,807 to 763,325 (approximately 3,519 base pairs). The gene is transcribed as part of a complex operon that includes the ribosomal protein genes `rplK` (Rv0668) and `rplA` (Rv0669), which are located immediately downstream. This operon structure is highly conserved across Actinobacteria and reflects the co-regulation of transcription and translation machinery components. The promoter region upstream of `rpoB` contains a canonical σ^A^ (SigA) -dependent promoter, which is the principal housekeeping sigma factor in Mtb. The promoter architecture includes a -10 box (TATAAT consensus) and a -35 box (TTGACA consensus) recognized by SigA, with additional upstream (UP) element sequences that enhance promoter strength through direct interaction with the RNAP α-subunit C-terminal domains.

### 1.2 Transcriptional Regulation and Promoter Architecture

The `rpoB` promoter is constitutively active but is subject to modulation by environmental stress conditions. Under conditions of oxidative stress, nutrient starvation, or exposure to cell wall-active antibiotics, the alternative sigma factor SigE (Rv1221) can partially redirect RNAP to stress-responsive promoters, but the `rpoB` promoter itself remains primarily SigA-dependent. DNase I footprinting experiments have identified a binding site for the transcriptional repressor FurA (Rv1909) in the upstream region of the `rpoB` operon, although the physiological relevance of this interaction is still under investigation. The 5' untranslated region (UTR) of the `rpoB` mRNA is relatively short (~50 nucleotides) and does not contain any known riboswitch elements. However, a putative RNA secondary structure near the ribosome binding site (Shine-Dalgarno sequence) may modulate translation efficiency in response to intracellular Mg^2+^ concentrations, providing a post-transcriptional regulatory layer.

### 1.3 Isoforms and Post-Transcriptional Modifications

Unlike eukaryotic genes, `rpoB` does not undergo alternative splicing. The gene is translated as a single polypeptide of approximately 1,178 amino acids (molecular weight ~128 kDa) in Mtb. However, the RpoB protein is subject to post-translational modifications that can influence its function. Mass spectrometry-based proteomic analyses have identified phosphorylation sites on RpoB, particularly on serine and threonine residues within the N-terminal region. The serine/threonine protein kinase PknB (Rv0014c) has been shown to phosphorylate RpoB *in vitro*, although the functional consequence of this modification on RNAP processivity or rifampicin binding remains to be fully characterized. Additionally, a naturally occurring N-terminal methionine excision occurs co-translationally, and the protein may undergo lysine acetylation, which is a common regulatory modification in mycobacteria.

### 1.4 Comparative Genomics and Orthologs

The `rpoB` gene is universally present in all bacterial genomes and is often used as a phylogenetic marker for species identification and taxonomic classification. In *Escherichia coli*, the orthologous gene is `rpoB` (b3987), encoding a 1,342-amino-acid protein. The Mtb RpoB shares ~65% sequence identity with the *E. coli* ortholog, with the highest conservation observed in the catalytic core and the rifampicin binding pocket. The gene is also present in archaea (as `rpoB` or `rpoB'` in some lineages) and in eukaryotic organelles (e.g., mitochondrial RNA polymerase in plants is encoded by the `rpoB`-like gene). In Mtb, there is no evidence of gene duplication or paralogs for `rpoB`, making it a single-copy essential gene. The essentiality of RpoB has been confirmed by transposon site hybridization (TraSH) and CRISPR interference (CRISPRi) screens, which classify `rpoB` as a growth-essential gene under standard *in vitro* culture conditions.

## 2. 3D Protein Domain Architecture & Structural Biology

### 2.1 Overall Architecture of the RNAP Holoenzyme

The bacterial RNAP holoenzyme is a multi-subunit complex with a total molecular weight of ~400 kDa. The core enzyme is composed of two α subunits (encoded by `rpoA`), one β subunit (RpoB), one β' subunit (RpoC), and one ω subunit (RpoZ). The holoenzyme additionally contains a sigma factor (σ) that directs promoter-specific binding. The overall architecture resembles a "crab claw" or "champagne cork" shape, with the β and β' subunits forming the two pincers of the claw. The active site, containing the catalytic Mg^2+^ ions, is located at the base of the cleft between the two pincers. The DNA template enters through a positively charged channel, and the RNA transcript exits through a separate channel.

### 2.2 Domain Boundaries of RpoB

The RpoB protein can be divided into several structurally and functionally distinct domains, numbered from the N-terminus to the C-terminus. The following domain boundaries are based on the crystal structure of the Mtb RNAP holoenzyme (PDB: 5UAC) and sequence alignments with *E. coli* RpoB.

| **Domain** | **Residue Range (Mtb)** | **Structural/Functional Role** |
| :--- | :--- | :--- |
| **N-terminal domain (NTD)** | 1–300 | Involved in interactions with the α subunit dimer and the σ factor; contributes to the assembly of the holoenzyme. Contains the "clamp" region that interacts with downstream DNA. |
| **Proximal domain** | 301–450 | Forms part of the RNA exit channel; interacts with the nascent RNA transcript and the transcription elongation factors NusA and NusG. |
| **Catalytic domain** | 451–700 | Contains the active site residues, including the conserved NADFDGD motif (residues 516–522 in Mtb) that coordinates the catalytic Mg^2+^ ions. This domain also forms the floor of the DNA/RNA hybrid binding channel. |
| **Rifampicin binding domain** | 701–850 | Forms the rifampicin binding pocket. This region is the primary target for rifampicin and is the site of most clinically relevant resistance mutations. |
| **C-terminal domain (CTD)** | 851–1178 | Involved in interactions with the β' subunit and the ω subunit; contributes to the stability of the core enzyme. Contains the "dock" domain that interacts with the σ factor region 4. |

### 2.3 The Rifampicin Binding Pocket

The rifampicin binding pocket is a deep, mostly hydrophobic cavity located at the base of the RNAP active-site cleft, adjacent to the DNA/RNA hybrid channel. The pocket is formed by amino acid residues from the Rifampicin binding domain (residues 701–850) and, to a lesser extent, from the catalytic domain. Key residues lining the pocket in Mtb include:

- **Gln 432** (Q432)
- **Met 434** (M434)
- **Asp 435** (D435)
- **His 445** (H445)
- **Ser 450** (S450)
- **Leu 452** (L452)
- **Ile 491** (I491)
- **Asn 493** (N493)
- **Leu 511** (L511)
- **Leu 512** (L512)
- **Asp 516** (D516)
- **Asn 518** (N518)
- **Ser 522** (S522)
- **Phe 523** (F523)
- **Arg 529** (R529)
- **Ile 572** (I572)
- **Leu 629** (L629)
- **Ser 631** (S631)

Rifampicin binds to this pocket through a network of hydrogen bonds and hydrophobic interactions. The naphthoquinone core of rifampicin forms a key hydrogen bond with the backbone carbonyl of Gln 432 and the side chain of His 445. The ansa chain of the drug wraps around the pocket, making contacts with residues in the 450–530 region. The binding of rifampicin physically occludes the path of the growing RNA transcript when it reaches a length of 2–3 nucleotides, thereby inhibiting transcription initiation and causing abortive initiation.

### 2.4 Structural Basis of Rifampicin Resistance

Mutations in the rifampicin binding pocket reduce the binding affinity of rifampicin for RNAP, thereby conferring resistance. The most common resistance mutations in Mtb are single nucleotide polymorphisms (SNPs) that result in amino acid substitutions at codons 516, 526, and 531 (using the *E. coli* numbering system, which is commonly used in the literature; the corresponding Mtb numbering is D435, H445, and S450, respectively). These mutations are located in the RRDR, which spans codons 507–533 (*E. coli* numbering) or approximately residues 426–452 in Mtb. The structural consequences of these mutations are:

- **S450L (Ser531Leu in *E. coli* numbering):** This is the most prevalent mutation, accounting for ~50-60% of rifampicin-resistant clinical isolates. The substitution of a serine with a bulky leucine residue introduces a steric clash with the naphthoquinone ring of rifampicin, significantly reducing drug binding.
- **H445Y/D (His526Tyr/Asp):** These mutations disrupt a critical hydrogen bond network between the histidine side chain and the ansa chain of rifampicin. The loss of this interaction reduces binding affinity by 10- to 100-fold.
- **D435V (Asp516Val):** This mutation alters the electrostatic environment of the pocket and disrupts a hydrogen bond with the rifampicin hydroxyl group.

### 2.5 Interactive 3D Visualizer

[Interactive 3D Protein Visualizer: Load rpoB (PDB: 5UAC)](/tools/protein-structure-viewer?source=direct&pdbId=5UAC)

The interactive visualizer allows users to explore the three-dimensional structure of the Mtb RNAP holoenzyme (PDB: 5UAC) in atomic detail. Users can highlight the RpoB subunit, color-code the rifampicin binding pocket residues, and visualize the position of rifampicin within the pocket. The visualizer also includes a sequence viewer that maps mutations onto the structure, enabling users to assess the structural impact of clinically relevant variants.

## 3. Cellular Signaling Pathways & Molecular Function

### 3.1 The Transcription Cycle

RpoB, as part of the RNAP core enzyme, is the central catalyst of transcription. The transcription cycle proceeds through three main phases: initiation, elongation, and termination.

1.  **Initiation:** The RNAP holoenzyme (core + σ factor) binds to promoter DNA, forming a closed complex. The DNA is then melted to form an open complex, and the first phosphodiester bond is synthesized. During this phase, RpoB contributes to the formation of the active site and the DNA-binding channel. The σ factor, which interacts with both RpoB and RpoC, is released upon transition to processive elongation.
2.  **Elongation:** The RNAP core enzyme translocates along the DNA template, processively synthesizing RNA at a rate of ~20–50 nucleotides per second in Mtb. RpoB forms the "secondary channel" through which NTP substrates enter the active site. The catalytic residues in the NADFDGD motif coordinate the Mg^2+^ ions that catalyze the nucleotidyl transfer reaction. RpoB also interacts with the RNA transcript in the RNA exit channel, and these interactions contribute to the stability of the transcription elongation complex.
3.  **Termination:** Transcription is terminated by either intrinsic (rho-independent) or rho-dependent mechanisms. Intrinsic termination involves the formation of a hairpin structure in the nascent RNA, which destabilizes the elongation complex. RpoB residues in the RNA exit channel are involved in sensing the hairpin and promoting complex dissociation.

### 3.2 Regulation of RpoB Expression and Function

The expression of `rpoB` is autoregulated at the transcriptional level. The RNAP holoenzyme containing the primary sigma factor SigA transcribes the `rpoB` operon. However, under conditions of high RNAP concentration, the enzyme can bind to a "secondary" promoter within the operon and repress its own transcription. This autoregulatory loop ensures that RNAP levels are maintained at a constant level relative to the growth rate.

Post-translational regulation of RpoB occurs through interactions with accessory proteins. The transcription elongation factors NusA (Rv0639) and NusG (Rv0638) bind to RpoB and modulate the processivity and pausing of RNAP. NusA binds to the proximal domain of RpoB and enhances transcriptional pausing, while NusG binds to the clamp domain and suppresses pausing. The small molecule alarmone (p)ppGpp, which is produced during the stringent response, binds to a site at the interface of RpoB and RpoC, leading to global changes in transcription initiation and elongation. This binding stabilizes the RNAP-DNA complex at certain promoters and destabilizes it at others, resulting in a reprogramming of gene expression that favors stress survival.

### 3.3 Protein-Protein Interaction Networks

RpoB is a hub in the protein-protein interaction network of the transcription machinery. High-throughput yeast two-hybrid and affinity purification-mass spectrometry (AP-MS) studies have identified dozens of interaction partners. Key interactions include:

- **RpoA (α subunit):** The N-terminal domain of RpoB interacts with the N-terminal domain of RpoA, contributing to the dimerization of the α subunits and the assembly of the core enzyme.
- **RpoC (β' subunit):** Extensive interactions between RpoB and RpoC form the main body of the RNAP. The C-terminal domain of RpoB interacts with the N-terminal region of RpoC, while the catalytic domains of both subunits come together to form the active site.
- **RpoZ (ω subunit):** The ω subunit binds to the C-terminal domain of RpoB and is required for optimal RNAP assembly and stability.
- **Sigma factors:** The primary sigma factor SigA interacts with a conserved region in the C-terminal domain of RpoB (the "σ-docking" site). Alternative sigma factors (e.g., SigE, SigH) compete for this site, allowing the cell to rapidly switch gene expression programs in response to stress.
- **GreA/GreB (transcription cleavage factors):** These factors bind to the secondary channel of RNAP and stimulate the intrinsic endonucleolytic cleavage activity of the enzyme, which is essential for resolving transcriptional arrest.

### 3.4 Mermaid Diagram: The Transcription Cycle and RpoB Interactions

```mermaid
flowchart TD
    A["RNAP Holoenzyme<br/>Core (α2ββ'ω) + σ"] --> B["Promoter Binding<br/>Closed Complex"]
    B --> C["DNA Melting<br/>Open Complex"]
    C --> D["Initiation<br/>Abortive Initiation"]
    D --> E["σ Release<br/>Promoter Clearance"]
    E --> F["Processive Elongation<br/>RpoB Catalytic Center"]
    F --> G["Pausing / Arrest<br/>GreA/GreB Rescue"]
    G --> H["Termination<br/>Intrinsic / Rho-dependent"]
    H --> I["RNAP Recycling"]
    I --> A

    subgraph "RpoB Interactions"
        J["RpoA (α)"] --> A
        K["RpoC (β')"] --> A
        L["RpoZ (ω)"] --> A
        M["σ Factor"] --> A
        N["NusA/NusG"] --> F
        O["(p)ppGpp"] --> F
    end
```

## 4. Pathogenic Hotspot Mutations & Clinical Differentials

### 4.1 The Rifampicin Resistance-Determining Region (RRDR)

The RRDR of RpoB is a hot spot for mutations that confer rifampicin resistance. This region spans codons 507 to 533 in the *E. coli* numbering system, which corresponds to residues 426 to 452 in the Mtb protein. Over 95% of rifampicin-resistant clinical isolates of Mtb harbor at least one mutation within this region. The mutations are predominantly missense substitutions, although small insertions or deletions (indels) have also been reported.

### 4.2 Common Mutations and Their Frequencies

The following table lists the most frequently observed RpoB mutations in rifampicin-resistant Mtb clinical isolates, along with their approximate frequencies and the level of resistance conferred.

| **Mutation (Mtb numbering)** | **Mutation (*E. coli* numbering)** | **Frequency (%)** | **RIF MIC (µg/mL)** | **Structural Consequence** |
| :--- | :--- | :--- | :--- | :--- |
| **S450L** | Ser531Leu | 50–60 | 32–64 | Steric clash with naphthoquinone ring; significant loss of binding affinity. |
| **H445Y** | His526Tyr | 10–15 | 16–32 | Disruption of hydrogen bond network with ansa chain. |
| **H445D** | His526Asp | 5–10 | 8–16 | Loss of hydrogen bonding; altered electrostatic environment. |
| **D435V** | Asp516Val | 5–8 | 8–16 | Disruption of hydrogen bond with rifampicin hydroxyl group. |
| **L452P** | Leu533Pro | 2–5 | 4–8 | Proline-induced kink in the polypeptide backbone; altered pocket geometry. |
| **Q432K** | Gln513Lys | 1–3 | 4–8 | Loss of hydrogen bond with rifampicin; introduction of positive charge. |
| **I491F** | Ile572Phe | 1–2 | 4–8 | Hydrophobic clash with the ansa chain. |
| **S450W** | Ser531Trp | 1–2 | 64–128 | Large aromatic side chain; severe steric clash. |

### 4.3 Low-Level Resistance and Disputed Mutations

Some mutations in the RRDR confer only low-level rifampicin resistance (MIC 0.5–2 µg/mL), which is below the critical concentration used in phenotypic drug susceptibility testing (DST). These "disputed" mutations, such as D435Y (Asp516Tyr), L452P (Leu533Pro), and H445N (His526Asn), can be missed by standard DST but are clinically significant because they can lead to treatment failure if rifampicin is used. The World Health Organization (WHO) has recently reclassified several of these mutations as "resistance-associated" and recommends that they be considered when designing treatment regimens.

### 4.4 Compensatory Mutations

In addition to the primary resistance mutations in the RRDR, Mtb can acquire secondary "compensatory" mutations that restore fitness costs associated with the primary mutation. These compensatory mutations are often found in the `rpoA` and `rpoC` genes, which encode the α and β' subunits of RNAP, respectively. For example, mutations in the β' subunit (e.g., V483G, I491T) have been shown to restore the transcriptional efficiency of RNAP carrying the S450L mutation in RpoB. The presence of compensatory mutations is associated with the transmission of MDR-TB strains, as they enable the resistant bacteria to compete with drug-susceptible strains in the absence of drug pressure.

### 4.5 Clinical Differentials and Diagnostic Implications

The detection of RpoB mutations is the basis for rapid molecular diagnostic tests for rifampicin resistance, such as the Xpert MTB/RIF assay (Cepheid) and the line probe assays (e.g., GenoType MTBDRplus). These assays target the RRDR and can detect the presence of mutations within hours, allowing for the rapid initiation of appropriate therapy. However, the presence of disputed mutations can lead to false-negative results in some assays, and the interpretation of results must be done in the context of the specific mutation detected. Next-generation sequencing (NGS) is increasingly being used to provide comprehensive information on the entire `rpoB` gene, as well as other resistance-associated genes, enabling the detection of both canonical and non-canonical resistance mutations.

## 5. Host-Pathogen & Viral Interactions (If applicable)

### 5.1 RpoB as a Target of Host Immune Responses

While RpoB is an intracellular bacterial protein and is not directly exposed on the bacterial cell surface, it can be released into the host environment upon bacterial lysis. RpoB is a highly immunogenic protein, and antibodies against RpoB have been detected in the sera of patients with active TB. These antibodies are not protective but can be used as biomarkers for diagnosis. Additionally, RpoB-derived peptides can be presented on MHC class II molecules by infected macrophages, leading to the activation of CD4+ T cells. However, the role of RpoB-specific T cell responses in protective immunity against TB is not well understood.

### 5.2 Interaction with Mycobacteriophages

Mycobacteriophages are viruses that infect mycobacteria, including Mtb. Some mycobacteriophages encode proteins that interact with the host RNAP to redirect transcription towards viral genes. For example, the mycobacteriophage Giles encodes a protein (Gp39) that binds to the β subunit of RNAP and acts as a transcription factor, activating the expression of middle and late viral genes. This interaction is highly specific to the mycobacterial RNAP and does not affect the host RNAP of other bacteria. The study of these phage-encoded RNAP-binding proteins provides insights into the evolution of transcription regulation and may lead to the development of novel anti-TB therapies.

### 5.3 RpoB in Non-Tuberculous Mycobacteria (NTM)

The `rpoB` gene is also used as a phylogenetic marker for the identification of non-tuberculous mycobacteria (NTM), such as *Mycobacterium avium* complex (MAC), *Mycobacterium abscessus*, and *Mycobacterium kansasii*. Sequence analysis of a 401-bp hypervariable region of the `rpoB` gene is a reliable method for species identification and is often used in clinical microbiology laboratories. Rifampicin resistance in NTM is less common than in Mtb but can occur through similar mechanisms, involving mutations in the RRDR. However, the specific mutations and their frequencies differ between species, and the clinical breakpoints for rifampicin susceptibility are species-specific.

## 6. [Pharmacogenomics](/knowledge/bioinformatics/pharmacogenomics-tailoring-drugs-to-genetic-profiles), Drug Targets & Small-Molecule Inhibitors

### 6.1 Rifampicin and Rifamycin Derivatives

Rifampicin (also known as rifampin) is a semisynthetic derivative of the rifamycin class of antibiotics, which are produced by the bacterium *Amycolatopsis rifamycinica*. Rifampicin is a first-line drug for the treatment of TB and is also used for the treatment of other mycobacterial infections, such as leprosy and MAC infections. The drug acts by binding to the RpoB subunit of RNAP and inhibiting transcription initiation. The binding site is highly conserved across bacterial species, but rifampicin has a narrow spectrum of activity, primarily targeting Gram-positive bacteria and mycobacteria.

Other rifamycin derivatives include:

- **Rifabutin:** A derivative with activity against both Mtb and *Mycobacterium avium* complex. Rifabutin is less potent than rifampicin but has a lower potential for drug-drug interactions due to its reduced induction of cytochrome P450 enzymes.
- **Rifapentine:** A long-acting derivative that is used in the treatment of latent TB infection and, more recently, in the treatment of drug-susceptible TB. Rifapentine has a longer half-life than rifampicin, allowing for once-weekly dosing.
- **Rifamycin SV:** An intravenous formulation used for the treatment of staphylococcal infections.

### 6.2 Cross-Resistance and Susceptibility Testing

Cross-resistance between rifampicin and other rifamycins is common but not absolute. Some RpoB mutations that confer resistance to rifampicin (e.g., S450L) also confer resistance to rifabutin and rifapentine. However, other mutations (e.g., D435V) may confer resistance to rifampicin but retain susceptibility to rifabutin. This differential susceptibility is due to the subtle differences in the binding modes of the different rifamycins. Phenotypic DST for rifabutin is recommended for isolates that are rifampicin-resistant but rifabutin-susceptible, as rifabutin may be a treatment option for these patients.

### 6.3 Novel RpoB Inhibitors

The emergence of rifampicin-resistant TB has spurred the development of novel inhibitors that target RpoB but bind to sites distinct from the rifampicin binding pocket. These inhibitors are designed to be active against rifampicin-resistant strains.

- **Sorangicin A:** A polyether antibiotic produced by the myxobacterium *Sorangium cellulosum*. Sorangicin A binds to the same pocket as rifampicin but makes different contacts with the protein. Some rifampicin-resistant mutants remain susceptible to sorangicin A, making it a promising lead compound.
- **CBR703 and related compounds:** These are inhibitors that bind to the "switch 2" region of RpoB, which is located near the active site. They inhibit transcription initiation by preventing the proper positioning of the DNA template. CBR703 and its analogs are active against rifampicin-resistant strains.
- **GE23077:** A cyclic peptide inhibitor that binds to the active site of RNAP and competes with NTP substrates. GE23077 is active against both rifampicin-susceptible and rifampicin-resistant strains.

### 6.4 Pharmacogenomic Considerations in TB Treatment

The [pharmacogenomics](/knowledge/bioinformatics/pharmacogenomics-tailoring-drugs-to-genetic-profiles) of rifampicin is primarily related to its effect on drug-metabolizing enzymes. Rifampicin is a potent inducer of the cytochrome P450 enzyme [CYP3A4](/knowledge/bioinformatics/genes/medical-genetics/cyp3a4-gene-structure-function-pathway), as well as other drug transporters and metabolizing enzymes. This induction can lead to significant drug-drug interactions, reducing the plasma concentrations of co-administered drugs, including antiretroviral drugs used for the treatment of HIV. The management of these interactions is a critical aspect of TB treatment, particularly in patients with HIV co-infection. The presence of RpoB mutations in the infecting Mtb strain is the primary determinant of rifampicin resistance, and the detection of these mutations is essential for guiding therapy.

## 7. Bioinformatic Resources & Database Accessions

The following table provides key database accessions and resources for the `rpoB` gene and its protein product.

| **Database** | **Accession / Identifier** | **Description** |
| :--- | :--- | :--- |
| **NCBI Gene** | 887169 (Rv0667) | Gene-specific information for *M. tuberculosis* H37Rv. |
| **Ensembl Bacteria** | Rv0667 | Genome browser view of the `rpoB` locus. |
| **UniProt** | P0A8V2 | Protein sequence, functional annotations, and post-translational modifications. |
| **RCSB PDB** | 5UAC | Crystal structure of the Mtb RNAP holoenzyme with rifampicin. |
| **Tuberculist** | Rv0667 | Comprehensive database for *M. tuberculosis* genes. |
| **Mycobrowser** | Rv0667 | Curated information on mycobacterial genes and proteins. |
| **Gene Ontology (GO)** | GO:0003677 (DNA binding), GO:0003899 (DNA-directed 5'-3' RNA polymerase activity), GO:0006351 (transcription, DNA-templated) | Functional annotations. |
| **STRING** | P0A8V2 | Protein-protein interaction network. |
| **BioGRID** | P0A8V2 | Physical and genetic interactions. |
| **ClinVar** | N/A (bacterial gene) | Not applicable for human clinical variants. |
| **CARD (Comprehensive Antibiotic Resistance Database)** | RpoB | Resistance gene ontology and mutation data. |

## Related Clinical & Scientific Guides

* [tpdA Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/microbiology-amr/tpda-gene-structure-function-pathway)
* [acm Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/microbiology-amr/acm-gene-structure-function-pathway)
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