The luria-latarjet effect studied by T4-lysozyme production

Abstract

The replication of bacteriophage T4 in Escherichia coli is sensitive to ultraviolet light (UV). The classical plaque assay shows a considerable increase in UV resistance starting at about 5 minutes after the bacteria are infected. Production of phage lysozyme starts about 10 minutes after infection and is sensitive to irradiation. Its UV resistance increases at about 4 minutes. The appearance of resistance, measured by both the plaque assay and lysozyme production, is inhibited by p-fluorophenylalanine. Resistance appears at the normal time in bacteria infected by a mutant phage amN116 whose major DNA synthesis is delayed beyond 20 minutes. These results suggest that the same event is responsible for resistance of both plaque formation and lysozyme production. The principal advantage of the lysozyme assay is that resistance can be detected more directly than with the plaque assay. Bacteria irradiated 7 minutes after infection were resistant when tested at 11 minutes. Resistance mechanisms that depend on gradual recovery after plating are ruled out by these results. So are mechanisms that require extensive DNA synthesis. The results are consistent with an event that takes place 5 minutes after infection and requires protein synthesis and at most a small quantity of DNA synthesis. They are in accord with a highly UV-sensitive switch from early to late functions being the principal initial target.