Interference of dna ts mutations of Escherichia coli with thymineless death

Abstract

Thermosensitive mutants of E.coli in which deoxyribonucleic acid replication is inhibited at high temperature have been assayed for their response to thymine deprivation at permissive and nonpermissive temperatures. The survival rate of mutants in which initiation of replication is defective at 42 C (dnaA and dnaC-D) is much higher at nonpermissive temperatures than at 32 C. By contrast, thymineless death is not hindered at 42 C in two elongation mutants dnaE and dnaG). Bacterial strains belonging to the dnaB class exhibit both types of behavior. These results are in accordance with the model linking thymineless death to a disruption of an active replication fork. The possibility that the dnaB protein takes part in this process of cell decay is discussed.