A mutant rho ATPase from Escherichia coli that is temperature-sensitive in the presence of RNA.

The Escherichia coli mutant rho-115 suppresses lac operon polarity conferred by the lacZ::IS1 insertion MS319. The ATPase activity of purified rho-115 protein was maximal at 40 degrees C, in contrast to 45 degrees C for rho+. At higher temperatures (50 degrees C, 55 degrees C), the fractions of activities at maximal temperature were consistently lower for rho-115 compared to rho+. The 30-minute time course of rho-115 ATP hydrolysis was linear at 37 degrees C but at 45 degrees C the linear kinetics of hydrolysis reached a plateau between 10 and 15 minutes. The 30-minute time courses for rho+ were linear at both 37 degrees C and 45 degrees C. The rho-115 and rho+ ATPase activities were equally heat-stable during preincubation at 45 degrees C in buffer. Inclusion of ATP during preincubation protected these rho proteins from inactivation to the same extent. The presence of polyC during preincubation protected rho+ activity but produced substantial inactivation of rho-115 ATPase. The presence of polyU during preincubation gave similar results. Concentrations of polyC between 625 ng/ml and 100 micrograms/ml yielded the same extent of rho-115 ATPase inactivation during preincubation at 45 degrees C. Thermal inactivation of rho-115 ATPase by polyC was halted by shifting preincubation temperature from 45 degrees C to 35 degrees C, indicating that polyC-induced destabilization of rho-115 was irreversible.