RpoD (sigma-70, sigma-A; PP_0387) is the primary (housekeeping/vegetative) sigma factor of Pseudomonas putida KT2440. As a dissociable, promoter-specificity subunit of RNA polymerase, it binds transiently to the RNAP catalytic core to form the holoenzyme and directs it to the majority of promoters used during exponential growth. RpoD belongs to the sigma-70 factor family (RpoD/SigA subfamily) and has the canonical multi-domain architecture: region 1.1 (autoinhibitory), region 2 (which contacts and melts the -10 promoter element to nucleate the open complex), region 3 (extended -10 recognition), and region 4 (which recognizes the -35 promoter element via a helix-turn-helix motif). After initiation it is released from the core enzyme. RpoD operates in the cytoplasm/nucleoid as part of the RNAP holoenzyme engaging chromosomal promoter DNA, and competition between RpoD and alternative sigma factors for a limiting pool of core RNAP is a major determinant of condition-dependent gene expression. Sigma factors are not catalytic enzymes; RpoD acts as a sequence- specific DNA-binding transcription initiation factor that establishes the housekeeping transcriptional program.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003677 DNA binding | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: RpoD binds promoter DNA via its conserved sigma-70 regions; region 4 recognizes the -35 element through a helix-turn-helix motif (annotated in UniProt at residues 576-595) and region 2 contacts the -10 element. DNA binding is a genuine, well-supported molecular activity. Reason: Correct but generic. The more specific and informative molecular function for this protein is sigma factor activity (GO:0016987), which captures the promoter-recognition role; DNA binding is retained as supporting but non-core. |
| GO:0003700 DNA-binding transcription factor activity | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: This InterPro2GO annotation assigns generic DNA-binding transcription factor activity. By GO convention bacterial sigma factors are not modeled as DNA-binding transcription factors (which act at specific operator sites); their function as the promoter-specificity subunit of RNA polymerase is captured by sigma factor activity (GO:0016987). Reason: Over-annotation arising from a broad InterPro-to-GO mapping. Sigma factor activity (GO:0016987) is the appropriate, mutually-exclusive molecular function for a sigma factor, so GO:0003700 should not be retained as a core function. |
| GO:0005737 cytoplasm | IEA GO_REF:0000120 | ACCEPT | Summary: RpoD acts in the cytoplasm/nucleoid as part of the RNA polymerase holoenzyme engaging chromosomal promoter DNA. Cytoplasmic localization is consistent with UniProt subcellular location and the function of a soluble RNAP subunit. Reason: Correct cellular component for a cytoplasmic RNA polymerase holoenzyme subunit; appropriate, if broad, localization annotation. |
| GO:0006352 DNA-templated transcription initiation | IEA GO_REF:0000120 | ACCEPT | Summary: RpoD is the sigma factor that confers promoter specificity for transcription initiation by RNA polymerase during exponential growth. This is the central biological process the protein participates in. Reason: Accurately describes the core process; directly supported by the conserved housekeeping sigma factor role. |
| GO:0006355 regulation of DNA-templated transcription | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: By determining which promoters are transcribed, RpoD regulates transcription. This is correct but a broad parent of the more specific transcription initiation process. Reason: True but general; the specific initiation processes (GO:0006352 and GO:2000142) better capture the core function. Retained as non-core. |
| GO:0010468 regulation of gene expression | IEA GO_REF:0000104 | KEEP AS NON CORE | Summary: A very broad biological process term reflecting RpoD's role in directing gene expression. Correct but high-level. Reason: Overly general grouping term; more specific transcription initiation terms describe the actual function. Retained as non-core. |
| GO:0016987 sigma factor activity | IEA GO_REF:0000120 | ACCEPT | Summary: Sigma factor activity is the precise molecular function of RpoD: it binds RNA polymerase core to form the holoenzyme and confers promoter recognition specificity. This is the defining, core molecular function. Reason: Most specific and informative molecular function term for this protein; strongly supported by family/domain architecture and the conserved housekeeping sigma role. |
| GO:2000142 regulation of DNA-templated transcription initiation | IEA GO_REF:0000108 | ACCEPT | Summary: Logically inferred from sigma factor activity (GO:0016987). RpoD regulates which promoters are recognized at the initiation step, so it regulates DNA-templated transcription initiation. Reason: Appropriate and consistent with the molecular function; captures the initiation-specific regulatory role of the housekeeping sigma factor. |
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Download this section (compressed HTML)Q: What is the genome-wide RpoD (sigma-70) regulon in P. putida KT2440, e.g. by ChIP-seq/ChIP-exo, and how does it overlap with alternative sigma factors?
Q: Is PP_0387 genetically essential in KT2440 (e.g. by conditional depletion), as expected for a primary sigma factor?
Experiment: ChIP-seq of RpoD-RNAP holoenzyme in exponentially growing KT2440 to define the sigma-70 promoter occupancy genome-wide.
Experiment: Conditional depletion or degron tagging of PP_0387 to test essentiality and characterize the transcriptional collapse upon RpoD loss.
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