A Large Insertion Domain in the Rho Factor From a Low G + C, Gram-negative Bacterium is Critical for RNA Binding and Transcription Termination Activity

Rho-dependent termination of transcription (RDTT) is a critical regulatory mechanism specific to bacteria. In subset species including most Actinobacteria and Bacteroidetes, the Rho factor contains large, poorly conserved N-terminal insertion domain (NID) cryptic function. To date, only two NID-bearing factors from high G + C have been thoroughly characterized. Both can trigger RDTT at promoter-proximal sites or with structurally constrained transcripts that are unsuitable for archetypal, NID-less Escherichia coli (EcRho). Here, we provide first biochemical characterization low bacterium. We show Bacteroides fragilis (BfRho) bona fide RNA-dependent NTPase motor able unwind long RNA:DNA duplexes disrupt complexes. The large NID (~40% total mass) strongly increases BfRho affinity RNA, strictly required RDTT, but does not promote transcript. Furthermore, preclude modulation by NusA NusG inhibitor bicyclomycin. Although prion-like Q/N-rich motif, it spontaneously formation β-amyloids. Thus, despite its unusually RNA binding domain, behaves more like EcRho than counterparts Actinobacteria. Our data highlight evolutionary plasticity Rho’s region illustrate how adapted distinct genomic contents.