Transcriptional control of two gene subclusters in the tRNA operon of bacteriophage T4

Publisher Website
Google Scholar
Abstract
In bacteriophage T4 DNA, transcription units recognized in vitro by host RNA polymerase consist of promotor-proximal ‘immediate early ’ (IE) genes and promotor-distal ‘delayed early ’ (DE) genes separated from each other by ρ-dependent transcription terminators1. In vivo, the transition from IE to DE transcription requires phage-specific protein synthesis and can be prevented by chloramphenicol (CAM)2. Most of the information about IE/DE transition has been obtained by hybridization analyses of mixtures of RNA species synthesized simultaneously on several T4 transcription units (for review see ref. 3). A useful model for the study of T4 gene expression at the level of primary transcripts and individual gene products is provided by the T4 tRNA operon, a cluster of genes coding for eight T4-specific transfer RNAs and two stable RNAs (species 1 and 2) of unknown function (Fig. 1). The 10 genes of the tRNA operon are arranged in two subclusters (I and II) with a promotor located about 1 kilobase pair upstream4,5. The primary transcripts and the final gene products of this region have been identified and isolated6,7. Moreover, this genetic region was recently cloned and a part of it sequenced5,8. We describe here the expression of T4 tRNA genes in vivo and in vitro in terms of the IE/DE concept and demonstrate that the two subclusters of the tRNA operon are subject to different modes of control.