Involvement of Other Bacteriophage T4 Genes in the Blockade of Protein Synthesis and mRNA Destabilization by a Mutation of Gene61.5

Abstract

Gene61.5of bacteriophage T4 is required for gene expression at late stages of infection; a mutant of gene61.5shows a reduced rate of synthesis of late proteins and accumulates short transcripts upon infection of nonpermissive host cells at 30°C (T. Kai, H. E. Sellick, and T. Yonesaki,Genetics144, 7–14, 1996). Here we describe that, although the defects are only apparent at late stages, gene61.5is expressed early after infection and that the requirement of a functional gene61.5is 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 gene61.5at high temperatures. Furthermore, we isolated five pseudorevertants of a gene61.5mutant, designated asssf1throughssf5,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 gene61.5in stabilizing mRNAs late in T4 infection.