Thermosensitive Mutants of Escherichia coli Unable to Propagate RNA Phage at 42 °C and Altered in Protein Synthesis

A procedure is described which can be employed to isolate the thermosensitive mutants of Escherichia coli affected in protein synthesis. The technique involves the enrichment of cells unable to propagate MS2 phage at 42 °C and the subsequent screening for thermosensitive growth and protein synthesis. Two of the mutants isolated in this way, QL‐152 and QL‐199, were studied in some detail. The synthesis of glutamyl‐tRNA by QL‐152 supernatant enzyme appeared to be thermosensitive. In the case of QL‐199 a 65% reduction of the glutaminyl‐tRNA synthesis was measured. Moreover QL‐199 cells contain an elongation factor EF‐Tu which is more thermolabile than wild‐type EF‐Tu.