Regulation of late functions in Salmonella bacteriophages P22 and L studied by assaying endolysin synthesis.

The rate of endolysin synthesis in Salmonella typhimurium cells infected by bacteriophage P22 or L was taken as a measure for the activity of 23 gene product (the positive regulator for the "late" genes of P22 and L). Endolysin in coded for by gene 19. The amber mutations in gene 23 of P22 and L, used in this study, reduced the rate of endolysin synthesis by a factor of ca. 90 for P22 and of ca. 20 for L. In mixed infections with 19- and 23- mutants the 23 gene products of P22 and L ACT As positive regulators for the respective gene 19 in cis and in trans. Cross-specificity of the 23 gene products, i.e., turning on expression of gene 19 on a chromosome of the other species, could not be demonstrated.