rho Factors from polarity suppressor mutants with defects in their RNA interactions.

rho proteins isolated from strains of Escherichia coli with the suA1, suA100, and suA120 polarity suppressor mutant alleles of the rho gene are shown to be defective in termination of T7 DNA transcription in vitro. These mutant rho factors are found to be less active than normal rho in catalyzing the hydrolysis of ATP with isolated T7 RNA as cofactor, and their lower ATPase activities correlate well with their decreased abilities to mediate release of RNA from isolated T7 DNA transcription complexes. The mutant rho factors also have lower ATPase activities than wild type rho with certain synthetic RNA polymers, but they have full activity with poly(C). Because the mutant rho factors have normal ATPase activity with some RNAs, we conclude that their defects are in their abilities to interact with certain RNA cofactors and not in their catalytic capacities. Binding studies indicate that their defects do not appear to involve the primary interaction between rho and RNA. When poly(dC) is used to saturate the primary site for RNA on rho, the Km values for (Cp)7C as a secondary site activator of rho ATPase are 3.4, 80, and 15 microM for rho from the strains with the wild type, suA1, and suA100 alleles, respectively. These results suggest that the defects in the rho factors isolated from strains with the polarity suppressor alleles suA1 and suA100 involve their abilities to interact with RNA at their secondary sites.