The archetypal gene transfer agent (RcGTA) is regulated via direct interaction with the enigmatic RNA polymerase omega subunit : Regulation of RcGTA production by GafA and Rpo-ω

Gene transfer agents (GTAs) are small virus-like particles that indiscriminately package and transfer any DNA present in their host cell, with clear implications for bacterial evolution. The first transcriptional regulator that directly controls GTA expression, GafA, was recently discovered but its mechanism of action remained elusive. Here we demonstrate that GafA controls GTA gene expression by direct interaction with the RNA polymerase omega subunit (Rpo-ω) and also positively autoregulates its own expression by an Rpo-ω independent mechanism. We show that GafA is a modular protein with distinct DNA and protein binding domains. The functional domains we observe in Rhodobacter GafA also correspond to two-gene operons in Hyphomicrobiales pathogens. Together these data allow us to produce the most complete regulatory model for a GTA, and point towards an atypical mechanism for RNA polymerase recruitment and specific transcriptional activation in the alpha-proteobacteria.