Mechanochemistry of transcription termination factor Rho.

Rho is a ring-shaped hexameric motor protein that translocates along nascent mRNA transcript and terminates transcription of select genes in bacteria. Using a numerical optimization algorithm that simultaneously fits all of the presteady-state ATPase kinetic data, we determine how Rho utilizes the chemical energy of ATP hydrolysis to translocate RNA. A random hydrolysis mechanism is ruled out by the observed inhibition of ATPase in a mixed hexamer containing wt and an inactive Rho mutant. We propose a mechanism in which (1) all six subunits are catalytically competent and hydrolyze ATP sequentially, (2) translocation of RNA is driven by the weak to tight binding transition of nucleotide in the catalytic site, (3) hydrolysis is coordinated between adjacent subunits by the transmission of stress via the catalytic arginine finger, (4) hydrolysis weakens the affinity of a subunit for RNA, and (5) the slow release of inorganic phosphate is controlled by changes in circumferential stress around the ring.