The δ subunit and NTPase HelD institute a two-pronged mechanism for RNA polymerase recycling
Cellular RNA polymerases (RNAPs) can become trapped on DNA or RNA, threatening genome stability and limiting free enzyme pools, but how RNAP recycling into active states is achieved remains elusive. In Bacillus subtilis, the RNAP δ subunit and NTPase HelD have been implicated in RNAP recycling. We structurally analyzed Bacillus subtilis RNAP-δ-HelD complexes. HelD has two long arms: a Gre cleavage factor-like coiled-coil inserts deep into the RNAP secondary channel, dismantling the active site and displacing RNA, while a unique helical protrusion inserts into the main channel, prying the β and β′ subunits apart and, aided by δ, dislodging DNA. RNAP is recycled when, after releasing trapped nucleic acids, HelD dissociates from the enzyme in an ATP-dependent manner. HelD abundance during slow growth and a dimeric (RNAP-δ-HelD)2 structure that resembles hibernating eukaryotic RNAP I suggest that HelD might also modulate active enzyme pools in response to cellular cues. The bacterial helicase-like transcription factor HelD interacts with the RNA polymerase (RNAP) and together with the RNAP δ subunit enhances RNAP cycling. Here, the authors present the cryo-EM structures of the monomeric and dimeric Bacillus subtilis RNAP-δ-HelD complexes and suggest a model for HelD/δ-mediated RNAP recycling and putative hibernation.
Published in: Nature Communications, 10.1038/s41467-020-20159-3, Springer Nature