USE OF A GENE ENCODING A SUPPRESSOR TRANSFER-RNA AS A REPORTER OF TRANSCRIPTION - ANALYZING THE ACTION OF THE NUN PROTEIN OF BACTERIOPHAGE-HK022

The Nun protein of phage HK022 blocks the expression of genes that lie downstream of the nut sites of phage lambda. Nun is believed to act b y promoting premature termination of transcription at or near these si tes. To test this hypothesis and to facilitate mapping the sites of te rmination, we inserted a gene encoding a suppressor tRNA immediately d ownstream of the lambda nutL site and determined the effect of Nun on tRNA level. We found that Nun severely reduced the accumulation of mat ure, biologically active tRNA and promoted the accumulation of short, promoter-proximal transcripts whose 3' ends were dispersed over a 100- nucleotide region downstream of nutL. These results are consistent wit h the hypothesis that Nun terminates transcription within the region i mmediately down-stream of nutL and are inconsistent with the hypothesi s that the only action of Nun is to prevent translation of genes locat ed downstream of the nut site. The stability, small size, and easily a ssayable biological function of suppressor tRNA recommend it as a repo rter of transcription in other systems.