norR1 encodes a nitric oxide-responsive sigma-54-dependent transcriptional activator in Cupriavidus necator H16. The protein has the conserved NorR domain architecture: an N-terminal GAF regulatory region, a central AAA+ ATPase domain, and a C-terminal Fis-family helix-turn-helix DNA-binding domain.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005524 ATP binding | IEA GO_REF:0000002 | MODIFY | Summary: NorR1 contains the conserved sigma-54-interaction/AAA+ ATPase region of bacterial enhancer-binding proteins. ATP binding is plausible, but ATP hydrolysis is the more informative molecular function for the transcriptional activation mechanism. Reason: The InterPro support identifies the sigma-54 interaction ATP-binding region, and NorR-family studies show that NO sensing stimulates NorR ATPase activity to activate transcription. Replace the generic binding term with ATP hydrolysis activity when making a positive MF assertion. Proposed replacements: ATP hydrolysis activity Supporting Evidence: file:CUPNH/norR1/norR1-uniprot.txt InterPro; IPR002078; Sigma_54_int. PMID:16193057 Binding of NO stimulates the ATPase activity of NorR, enabling the activation of transcription by RNA polymerase. |
| GO:0006355 regulation of DNA-templated transcription | IEA GO_REF:0000002 | MODIFY | Summary: NorR1 positively activates NO-responsive transcription of the norAB nitric oxide reductase operon through a sigma-54-dependent promoter. Reason: The existing term is correct but too general. Species-specific Ralstonia evidence shows NorR is required for transcriptional activation of norA1/ norB1 in response to NO, and promoter-site mutations strongly reduce activation. Proposed replacements: positive regulation of DNA-templated transcription Supporting Evidence: PMID:11069685 norB1 gene transcription requires a functional rpoN gene and the regulator NorR, a novel member of the NtrC family of response regulators. PMID:15667304 norB and the adjacent norA form an operon that is controlled by the sigma(54)-dependent transcriptional activator NorR in response to NO. |
| GO:0043565 sequence-specific DNA binding | IEA GO_REF:0000002 | MODIFY | Summary: NorR1 binds regulatory DNA upstream of the nitric oxide reductase operon, but sequence-specific DNA binding alone is an under-specified molecular function for this protein. Reason: NorR is an NO-responsive, sigma-54-dependent transcriptional activator. The literature supports both DNA binding to upstream activator sequences and ligand-modulated activation, so GO:0141097 is a better MF endpoint than generic sequence-specific DNA binding. Proposed replacements: ligand-modulated transcription activator activity Supporting Evidence: PMID:15667304 A NorR derivative containing MalE in place of the N-terminal domain binds to a 73 bp region upstream of norA that includes three copies of the putative upstream activator sequence GGT-(N(7))-ACC. PMID:16193057 The NO-responsive activity of NorR raises important questions concerning the mechanism of NO sensing. |
| GO:0019333 denitrification pathway | IEA GO_REF:0000041 | MARK AS OVER ANNOTATED | Summary: NorR1 regulates nitric oxide reductase expression, but it is not itself a denitrification enzyme. UniProt explicitly marks the denitrification pathway association as regulation. Reason: Species-specific evidence supports a regulatory role limited to NO-responsive nitric oxide reductase transcription. The PMID:11069685 abstract states that other nitrogen oxide-reducing steps are independent of NorR, so projecting a direct denitrification-pathway annotation to NorR1 overstates the gene product's role. Supporting Evidence: file:CUPNH/norR1/norR1-uniprot.txt PATHWAY: Nitrogen metabolism; nitrate reduction (denitrification) [regulation]. PMID:11069685 This reaction is not strictly co-ordinated on the regulatory level with the other nitrogen oxide-reducing steps of the denitrification chain that are independent of NorR. |
| GO:0141097 ligand-modulated transcription activator activity | IMP PMID:11069685 A novel NO-responding regulator controls the reduction of ni... | NEW | Summary: NorR1 is an NO-responsive transcriptional activator of the nitric oxide reductase operon. Reason: This term captures the complete NorR molecular activity better than the separate automated ATP-binding and sequence-specific DNA-binding terms. Ralstonia-specific mutant/reporter evidence establishes NO-responsive transcriptional activation, while broader NorR-family biochemical work explains the ligand-modulated AAA+ activation mechanism. Supporting Evidence: PMID:11069685 Transcription activation by NorR responds to the availability of NO. PMID:15667304 Mutations altering individual bases of this sequence resulted in an 80-90% decrease in transcriptional activation by wild-type NorR. PMID:16193057 Here we show that the regulatory domain of NorR contains a mononuclear non-haem iron centre, which reversibly binds NO. file:CUPNH/norR1/norR1-deep-research-falcon.md Falcon synthesis identifies NorR1 as an NO-sensing sigma-54 bacterial enhancer-binding protein with GAF, AAA+ ATPase, and DNA-binding domains, activating norAB transcription rather than catalyzing a denitrification reaction. file:interpro/panther/PTHR32071/PTHR32071-deep-research-falcon.md PTHR32071 family research supports sigma-54 enhancer-binding proteins as conserved AAA+ ATPase transcriptional activators whose specific biological-process wiring depends on N-terminal sensory/regulatory domains. |
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