Analysis of expression of the rII gene function of bacteriophage T4

Abstract

Temperature-sensitive (ts) mutants of the T4 phage rII gene were isolated and used in temperature shift experiments that revealed two different expressions for the normal rII (rII+) gene function in vivo: (i) an early expression (O to 12 min postinfection at 30 C) that prevents restriction of T4 growth in Escherichia coli hosts lysogenic for X phage, and (ii) a later expression (12 to 18 min postinfection at 30 C) that results in restriction of T4 growth when the phage DNA ligase (gene 30) is missing. The earlier expression appeared to coincide with the period of synthesis of the protein product of the T4 rIlA cistron, whereas the later expression occurred after rIIA protein synthesis had stopped. The synthesis of the protein product of the rIIB cistron continues for several minutes after rIIA protein synthesis ceases (O'Farrell and Gold, 1973). The two rII+ gene expressions might require different molar ratios of the rIIA and rIlB proteins. It is possible that the separate expressions of rII + gene function are manifestations of different associations between the two rII proteins and other T4-induced proteins that are synthesized or activated at different times after phage infection. The rII gene of bacteriophage T4 consists of two contiguous cistrons, rIIA and rIIB, the functions of which have not been explained. Mutations in either cistron can result in a number of effects on the physiology of phage growth in infected Escherichia coli hosts. Two types of observations suggest that the rII gene products play roles in T4 DNA metabolism. (i) T4 rII mutants do not propagate in E. coli hosts that are lysogenic for phage X (2). It appears that normal T4 rII (rII+) gene function is required to prevent the inhibition of T4 DNA replication that is caused, at least in part, by the rex gene function of X prophage (1, 10, 11, 22, 26). (ii) T4 rII mutants can replicate their DNA and produce high yields of phage without the DNA ligase coded by T4 gene 30 (4, 6, 12). It