DESTABILIZATION OF BACTERIOPHAGE-T4 MESSENGER-RNAS BY A MUTATION OF GENE-61.5

Mr, identified a novel gene of bacteriophage T4, gene 61.5, which appe ars to be involved in protein synthesis late in infection. Northern bl ot analysis revealed that a mutant of 61.5 accumulated truncated trans cripts of representative late genes. Using a double mutant of genes 61 .5 and 55, which prevents transcription of late genes, we demonstrate that even transcripts of middle genes, while full-length when initiall y expressed, are similarly truncated at later stages of infection. The se results indicate that the abnormality in transcript length occurs l ate in infection, regardless of whether the transcript derives from a middle or a late gene. Primer-extension analysis revealed that the 5' ends of the late gene 23 transcripts that accumulated in gene 61.5 mut ant-infected cells were located at internal discrete sites as well as at the expected transcription start site. Moreover, the decay rates of full-length transcripts from genes uvsY or 45 were more than twofold faster in the absence of a functional gene 61.5. These results suggest that mutation of gene 61.5 activates endonucleolytic cleavage of midd le and late transcripts, probably by RNase M.