Structural basis of HutP-mediated transcription anti-termination

Bacteria often use anti-terminator proteins to sense a specific metabolite signal and direct RNA polymerase to either terminate transcription or transcribe the downstream genes of an operon. Although many proteins that regulate various operons using this mechanism have been identified, insights into their activation processes before cognate mRNA binding have remained obscure. HutP from Bacillus subtilis regulates the hut operon by an anti-termination mechanism. Recently, several crystal structures of HutP [apo-HutP, HutP-L-histidine (and histidine analog), HutP-L-histidine-Mg(2+) and HutP-L-histidine-Mg(2+)-RNA] have been reported. These structural and functional studies of HutP have revealed how the protein undergoes conformational changes in response to two key components: L-histidine and Mg(2+) ions.