RNA remodeling by hexameric RNA helicases.

The unwinding of RNA helices and the disruption of RNA-protein complexes are critical steps of cellular metabolism that are carried out by ubiquitous NTP-dependent enzymes named RNA helicases. Here, we review the structures, mechanisms, and biochemical properties of two RNA helicases known to adopt a homo-hexameric ring architecture: the P4 packaging motor of bacteriophage φ8, a Super-Family 4 helicase, and Escherichia coli's transcription termination factor Rho from the Super-Family 5 of helicases. We emphasize the many similarities as well as key differences that characterize the Rho and P4 motor mechanisms and highlight important questions that remain to be addressed.