Phenotypic reversion by 5-fluorouracil of Amber mutations in bacteriophage T4: Characterization of rescued functions

Abstract

Phenotypic reversion by 5-fluorouracil of amber mutations in phage T4 was studied. The rescued functions of the early genes 1 (deoxynucleotide kinase), 42 (deoxycytidylate hydroxymethylase) and 56 (deoxycytidine triphosphatase) were investigated by direct measurements of the rescued enzyme activities. Addition of 5-fluorouracil early (2 min after infection) but not late (16 min) was effective in rescuing enzyme activities corresponding to the mutated genes. The time course of formation of the rescued enzymes was similar to that of other early enzymes in nonpermissive bacteria after DNA-negative mutant infection: Enzyme activity increased for 10–15 min beyond the time of shut-off in wild-type T4-infected cells. These results indicate that transcription of the mutated early genes, rather than the translation of early messengers, is restricted in the late period of infection with early amber mutants.