Suppression of T4D ligase mutations by rIIa and rIIb mutations.

The introduction of rII mutations into polynucleotide ligase amber mutants (gene 30) of T4D bacteriophage results in the restoration of phage growth in the nonpermissive host E. coli B. When cells are mixedly infected with rII(+) -ligase(-) and rII-ligase(-) phage, growth is reduced, indicating that the rII mutations are recessive to the rII(+) alleles. Infection with the rII-ligase(-) double mutants results in nearly complete restoration of phage DNA synthesis and prevents the extensive degradation of parental phage DNA observed after infection with ligase(-) single mutants. Similar results are observed when cells are infected with ligase(-) mutants and chloramphenicol is added five minutes post infection.