Loading Rho to Terminate Transcription

In bacteria, one of the major transcriptional termination mechanisms requires a hexameric RNA/DNA helicase known as Rho. One question that has remained unanswered is how the helicase loads onto a nascent transcript so that it can initiate actions on the transcript to cause termination. Recent structures of Rho bound to nucleic acid by show how the individual RNA-binding domains of the 6 subunits are organized and that the ring is split open. The opening is wide enough to accommodate single-stranded RNA and suggests that this conformation is poised to load onto mRNA.