Escherichia coli Strains with Thermolabile Ribonuclease II Activity

Studies with ribonuclease II enzymes from various temperature sensitive Escherichia coli mutants that showed heat labile ribonuclease II activity in extracts indicated that only one of these strains, 1113B, contains an altered heat labile ribonuclease II enzyme. Genetic analysis of temperature independent transductants indicated that strain 1113B carries two mutations that cause a decrease in its capacity to grow at elevated temperatures. However, neither of these mutations is responsible for the altered ribonuclease II in this strain. Moreover, strains with this altered RNase II enzyme are capable of growing exponentially at 45°, and growth at that temperature (45°) does not affect their level of ribonuclease II.