In Escherichia coli B infected with phage T4 with mutations in gene 55 the shut-off of synthesis of two early enzymes was found to be delayed 10 to 15 min as compared to wild-type T4 infection. The kinetics of early enzyme formation was very similar to that obtained after DNA-negative mutant infection. The transcription of gene 1 (one of the genes coded for early enzymes) ceased at 9 to 12 min after infection whether the gene 55 product was active or not, as determined by the time dependence of fluorouracil rescuability of DNA synthesis in cells infected with a gene 1 amber mutant. The synthesis of the major part of the early RNA species, determined by pulse-labeling with uracil-5-(3)H, was furthermore found to be regulated independently of gene 55. An explanation for the extended early enzyme synthesis in DNA-negative and gene 55 mutant infection is offered: translation of early messengers is restricted after about 12 min in wild-type infection, whereas in cells infected with DNA-negative or gene 55 mutants, i.e., the absence of late protein synthesis, early messengers direct the formation of early enzymes for a longer time.