Induction of the SOS system by DNA ligase-deficient growth of Escherichia coli

When Escherichia coli carrying a thermosensitive mutation in DNA ligase was grown at the restrictive temperature, several functions associated with the SOS system were induced. These included lambda prophage induction, W-reactivation and W-mutagenesis of ultraviolet-irradiated lambda phage, and recA protein synthesis, all of which were lexA+ recA+ recB+ dependent and chloramphenicol sensitive, and lexA+-dependent filamentation. These results indicate that ligase-deficient growth leads to the induction of the SOS system, and that all the above functions may respond to common induction signals.