LactobacilIus lactis cells were infected with the bacteriophage 0LL55. The changes in DNA, RNA and protein synthesis were studied by following a long-term (over 3 h) incorporation of radioactive precursors into acid-insoluble material. Stimulation of DNA synthesis caused by phage occurred 30-35 rain after infection and thymidine incorporation continued for about 70 rain ceasing 1 0 -20 rain before the cells started to lyse. Cumulative (t4C)-uracil incorporation into RNA continued at the level of uninfected cells for 3 0 -4 0 min before starting to slow up. Protein synthesis in the infected cells followed that of a control culture for 4 0 -5 0 rain before the further incorporation of (l~C)-leucine began to decrease.
The additions of antibiotic inhibitors of RNA and protein synthesis (rifampicin and chloramphenicol, respectively) at various times before or during the prereplicative period showed that rifampicin, added up to 15 rain after infection and chloramphenicol, added as late as 2 0 -25 rain after infection completely prevented the initiation of phage-genome replication. The later addition of these drugs did not prevent the out-burst of thymidine up-take, but promoted, however, a deduction in the initiations of new replication cycles. The results indicate that certain genes of 0LL55 genome must be expressed at the early stages of infection to confirm a proper onset and continuation of phage DNA replication.