The Selective Inhibition of Protein Initiation by T4 Phage-Induced Factors

Abstract

Abstract. The phenomenon of selective translation of T4 template RNA by ribosomes from T4-infected cells, or factors derived therefrom, has been extended to studies on the initiation of protein synthesis. A high-salt extract derived from T4-infected ribosomes inhibits the formation of initiation complexes of MS2 and Escherichia coli template RNA with uninfected ribosomes while efficiently supporting the formation of initiation complexes with T4 template RNA. T4 factors also permit T5 template RNA to bind to E. coli ribosomes, which indicates that the T4 selective effect is not exclusive for T4 templates. Other evidence indicates that T4 factors do not alter the process of polypeptide chain elongation.Various reports have now described specific changes in the translational machinery of E. coli when infected by T-even bacteriophage. These changes include alterations in host tRNAs'-3 and the enzymes which modify them,4'5 changes in aminoacyl-tRNA synthetases,6 and the synthesis of phage-coded tRNAs.7-9 Another induced alteration was found by Hsu and Weiss,'0 who observed that ribosomes from T4-infected cells efficiently translate T4 template RNA but are restricted in their translation of host and MS2 RNA's. This phenomenon is an early phage function and is not manifested when infection occurs in the presence of chloramphenicol'0 or with T4 ghosts (unpublished results of the authors).In the same report, Hsu and Weiss found that a high-salt extract of T4-infected ribosomes (T4 factors) imparts a similar property of "selective" T4 RNA translation when added to uninfected ribosomes. These findings were interpreted by the authors as a form of translational control exerted by the invading phage on its host. Subsequent reports by Schedl et al.,1' Dube and Rudland,"2 and Steitz et al.'3 confirm the above observations. Refs. 12 and 13 also show that T4 factors restrict the binding of host, f2, and R17 RNA to ribosomes but permit the binding of T4 RNA. In this communication, we provide independent evidence that T4 factors exert their restrictive effect at the level of the formation of initiation complexes, and that the apparent selective translation of T4 template RNA, in vitro, is not exclusive. In addition, evidence is presented which indicates that T4 factors exert no effect on the elongation of polypeptide chains.

System of Double Infection Between Vaccinia Virus and Mengovirus

“…Mengovirus might also interfere with the synthesis of late vaccinia virus messenger RNA, once early messenger and early proteins were apparently synthesized. It may be, however, that each virus produces a "translation inhibitory protein" similar to that described in bacterial cells infected with T-even phages (8,9,11,17,26). If such was the case, the ribosomes of the cell would eventually be unable to synthesize effectively either host, mengovirus or vaccinia virus proteins, and the result would be the double interference reported here.…”

Inhibition of Replication of Ribonucleic Acid Bacteriophage f2 by Superinfection with Bacteriophage T4

“…It is difficult to decide between these alternatives. Most workers favor the second mechanism, largely because of experiments in which it was shown that ribosomes isolated from cells 12 min after T4 infection were unable to translate or bind f2 RNA, but could translate normally poly uridylic acid or late T4 mRNA (5,16,19). These cell-free experiments must be interpreted with caution.…”

“…Infection of Escherichia coli by the deoxyribonucleic acid (DNA) phage T4 results in cessation of host ribonucleic acid (RNA) and protein synthesis. Mechanisms proposed to account for this include alterations in the host membrane (6,8), synthesis of a T4-specific factor for initiation of transcription (30), a loss of certain host transfer RNA (tRNA) species (29) with replacement by phage-specific tRNA species (4,28), and a change in the factors required for initiation of messenger translation (5,16,19,20).…”

T4 Transfer RNAs: Codon Recognition and Translational Properties

“…The assigned codons for leucine are UUA, UUG, CUU, CUC, CUA, and CUG. The reaction system was essentially the same as described by Klemi et al (11) except that no added tRNA was present. An S165 soluble supernatant fraction, derived from 1/4 log E. coli B cells, was treated with DEAE-cellulose to remove endogenous tRNA and dialyzed (14).…”