A Mutant of Bacteriophage T7 Deficient in Polynucleotide Ligase

Abstract

Abstract An amber mutant of bacteriophage T7, obtained by mutagenesis with hydroxylamine, fails to induce the T7 polynucleotide ligase upon infection of Escherichia coli. The mutant (T7amHA13) grows normally on a suppressor-negative host; its sensitivity to ultraviolet light is the same as that of wild type T7. The DNA synthesized upon infection of E. coli by T7amHA13 is identical with that synthesized after infection by wild type phage, as measured by sedimentation in alkaline sucrose gradients. However, T7amHA13 does not grow in a ligase-deficient mutant of E. coli, E. coli N1318. Small fragments (11 S) of DNA accumulate after T7amHA13 infection of N1318, suggesting that the T7 ligase plays a role in DNA replication, but that the wild type host can supply sufficient ligase activity for growth of phage T7.