Evidence for an early regulatory function in phage P22

Summary A temperature sensitive mutant of P22 phage (ts X) was isolated and studied.This mutant seems to have a basic regulatory function: it is defective in an early function like the typical DNA^- mutant ts 12.1; it is unable to direct the phage DNA synthesis and does not lyse infected or induced cells.Unlike ts 12.1, the mutation ts X seems to involve a gene product necessary for the expression of any vegetative function, since no phage protein synthesis, no alteration of host DNA synthesis, and no cell killing can be observed under non-permissive conditions.The possible functional similarity between the N-cistron of the phage and the present X-cistron in P22 is discussed.