Transcription factors respond to multi-level stimuli and co-occupy promoter regions of target genes to activate RNA polymerase (RNAP) in a cooperative manner. Multiple transcription factors act in concert via co-occupying the promoter regions and respond to different input signals to precisely control the transcription output of downstream genes in both prokaryotes and eukaryotes. In bacteria, one global regulator and one context-specific regulator usually function as a pair to activate gene transcription in a cooperative manner. Carbon/nitrogen (C/N) balance control is critical to maintain the cellular homeostasis for all organisms. As an ancient photoautotrophic bacterium, cyanobacteria have evolved a finely regulated signal transduction network to keep pace of nitrogen assimilation with CO2 fixation. The global regulator NtcA in the catabolite activator protein (CAP) family plays a central role in maintaining the C/N balance through sensing the central metabolite 2-oxoglutarate. Cyanobacteria mainly utilize the nitrate assimilation pathway encoded by nirA-nrtABCD-narB operon to import and reduce nitrate. The expression of nirA operon is maintained at basal level by the global regulator NtcA and boosted by the context-specific activator NtcB. Therefore, the regulation of nirA operon by NtcA and NtcB serves as an excellent model for studying cooperative transcription activation in bacteria. Here you can see a very recent cryoEM structure of the full transcription activation complex NtcA-NtcB-TAC from Anabaena (PDB code: 8H3V)

#molecularart ... #proteinimager ... #cryoem ... #anabaena ... #activation ... #complex ... #nirA

Structure rendered with @proteinimager and depicted with @corelphotopaint