Expression of bacteriophage T4 genes 45, 44, and 62 I. Discoordinate synthesis of the T4 45- and 44-proteins

Abstract

T4 genes 45, 44, and 62 code for proteins that play essential roles in phage DNA replication. These three genes map as a cluster on the T4 chromosome and are thought to be transcribed into one polycistronic mRNA. We reexamined the possibility that these three genes are cotranscribed and obtained results which suggested that the protein products of genes 44 and 62 are translated from one mRNA species, but that the protein products of genes 45 and 44 are translated from different mRNA species. Cotranscription of T4 genes 44 and 62 was implied by polar effects that two amber mutations in gene 44 exhibited on the synthesis of the protein product of gene 62. In contrast, an amber mutation in T4 gene 45 did not affect the synthesis of the protein products of genes 44 and 62, and the protein products of genes 45 and 44 were found to be disproportionately synthesized under more than one type of growth condition. In the accompanying paper, Bowles and Karam present genetic evidence for the existence of a regulatory site for gene 44 that does not service gene 45. This also suggests that genes 45 and 44 belong to different operons. The T4 gene 45 amber mutation that we used in our studies exhibited a cis-dominant effect on the biological activity (although not on the synthesis) of a partially defective protein product of gene 44. The results suggest that the protein products of genes 45 and 44 are more likely to interact with each other in vivo when they are coded for by the same genome than when they are synthesized from genotypically different coinfecting genomes.