Regulation of transcriptional pausing through the secondary channel of RNA polymerase.

Transcriptional pausing has emerged as an essential mechanism of genetic regulation in both bacteria and eukaryotes, where it serves to coordinate transcription with other cellular processes and to activate or halt gene expression rapidly in response to external stimuli. Deinococcus radiodurans, a highly radioresistant and stress-resistant bacterium, encodes three members of the Gre family of transcription factors: GreA and two Gre factor homologs, Gfh1 and Gfh2. Whereas GreA is a universal bacterial factor that stimulates RNA cleavage by RNA polymerase (RNAP), the functions of lineage-specific Gfh proteins remain unknown. Here, we demonstrate that these proteins, which bind within the RNAP secondary channel, strongly enhance site-specific transcriptional pausing and intrinsic termination. Uniquely, the pause-stimulatory activity of Gfh proteins depends on the nature of divalent ions (Mg(2+) or Mn(2+)) present in the reaction and is also modulated by the nascent RNA structure and the trigger loop in the RNAP active site. Our data reveal remarkable plasticity of the RNAP active site in response to various regulatory stimuli and highlight functional diversity of transcription factors that bind inside the secondary channel of RNAP.