Gene 61.5 of bacteriophage T4 is required for gene expression at late stages of infection; a mutant of gene 61.5 shows a reduced rate of synthesis of late proteins and accumulates short transcripts upon infection of nonpermissive host cells at 30 degreesC (T. Kai, H. E. Sellick, and T. Yonesaki, Genetics 144, 7-14, 1996). Here we describe that, although the defects are only apparent at late stages, gene 61.5 is expressed early after infection and that the requirement of a functional gene 61.5 is partially compensated by the passage of early and middle stages of infection at high temperatures, suggesting that T4 genes expressed at early and middle stages bypass the requirement for the gene 61.5 at high temperatures. Furthermore, we isolated five pseudorevertants of a gene 61.5 mutant, designated as ssf1 through ssf5, which partially restored the growth ability at low temperatures, stabilized mRNAs, and stimulated protein synthesis at late stages. These results strongly suggest that the products of other T4 genes interact with the product of gene 61.5 in stabilizing mRNAs late in T4 infection.
Copyright 1998 Academic Press.