Effect of chloramphenicol and starvation for an essential amino acid on the synthesis and decay of T4 bacteriophage-specific messengers transcribed from early and quasi-late promoters

Abstract

Results of experiments in which the interval between infection and addition of rifampicin was varied indicated that messengers for T4 phage-specific dihydrofolate reductase, dCMP hydroxymethylase, both glucosyltransferases, DNA methylase, dCMP deaminase, and deoxycytidine triphosphatase are transcribed uniquely from early promoters (i.e., promoters that start to function moments after infection). In contrast, messengers for deoxynucleoside monophosphate kinase are transcribed exclusively from a quasi-late promoter (i.e., a promoter that does not function until 2 min postinfection). Messengers for DNA polymerase and dTMP synthetase are transcribed from both kinds of promoters. Transcription from early (P E) and quasi-late (P Q) promoters was studied under conditions that limit phage-specific protein synthesis to 5 or 10% of its normal maximum value. The conditions employed were treatment with chloramphenicol and starvation for an essential amino acid (in this case, leucine). Accumulation of viral-coded messengers was monitored by the ability of RNA made in vivo to sustain specific enzyme synthesis when rifampicin, a potent inhibitor of the initiation of RNA synthesis, was added prior to the restoration of protein synthesis. During treatment with chloramphenicol or starvation for an essential amino acid, RNA chains were initiated exclusively at P E'S. However, chloramphenicol limited transcription to presumed P E-proximal genes whereas P E-proximal and distal genes were transcribed during starvation for an essential amino acid. Under both conditions, the transcriptive yield from P E's was subnormal. In leucine-supplemented hosts, P E-distal and P Q transcription became chloramphenicol-refractile by the second minute. On the other hand, P E-distal transcription remained chloramphenicol-sensitive until the fourth minute in leucine-depleted hosts. Global T4 prereplicative messengers decayed with a functional half-life of 8–9 min in both leucine-supplemented and starved hosts. In both cases, decay followed simple exponential kinetics until, at least, 1% survival. Chloramphenicol stabilized most messengers in both supplemented and starved hosts. When chloramphenicol was added 4 min after infection of leucine-supplemented hosts, messengers transcribed from P E's were stablized but messengers transcribed from P Q's were not. About 50% of the decay of P Q-initiated messengers in chloramphenicol was due to the suA nuclease. The data are discussed in terms of the interrelationship between postinfection protein synthesis and prereplicative transcriptive events in bacteriophage T4.