Inhibition of host protein synthesis during infection of Escherichia coli by bacteriophage T4. II. Induction of host messenger ribonucleic acid and its exclusion from polysomes

Abstract

Two gene clusters on the Escherichia coli chromosome were induced at early times after T4 infection when >99% of the cells were infected: the lactose (lac) operon and prophage lambda. Their messenger ribonucleic acid (mRNA) was detected by hybridization to phi80 dlac deoxyribonucleic acid (DNA) and lambdaDNA, respectively. Synthesis of host mRNA could be initiated during the first few minutes after T4 infection, although no beta-galactosidase activity could be detected. Hybridization analyses of selected fractions from sucrose gradients revealed that most of this lac mRNA induced at very early times of T4 infection was not associated with ribosomes. In contrast, virtually all lac mRNA in uninfected bacteria was associated with polysomes. This exclusion affected all host mRNA; about 70% of E. coli(3)H-mRNA, labeled from 2 to 3 min after T4 infection, was excluded from polysomes. Infection even reduced the yield of beta-galactosidase from lac mRNA induced before infection. Gradients from rifampicin-inhibited cells showed the normal growth of lac mRNA polysomes; in contrast, T4 infection prevented growth of the preinduced lac polysomes. It is concluded that T4 infection interferes within seconds with the reassociation of ribosomes to host mRNA.