THE LATE-EXPRESSED REGION OF THE TEMPERATE COLIPHAGE-186 GENOME

The late-lytic region of the genome of bacteriophage 186 encodes the p hage proteins that synthesize the complex viral particle and lyse the bacterial host. We report the completion of the DNA sequence of the la te region and the assignment of 18 previously identified genes to open reading frames in the sequence. The 186 late region is similar to the late region of phage P2, sharing 26 genes of known function: the sing le gene for activation of late gene transcription, 6 genes for constru ction of DNA-containing heads, 16 for tail morphogenesis, and 3 for ce ll lysis. We identified two 186 late genes with unknown function; one is homologous to previously unrecognised genes in P2, HP1, and phi CTX , and the other may modulate DNA packaging. The 186 late region, like the rest of the genome, lacks the lysogenic conversion genes that are carried by P2, allowing the 186 late region to be transcribed from onl y three late promoters rather than four. The relative absence of lysog enic conversion genes in 186 suggests that the two phages have evolved to use the lytic and lysogenic reproductive modes to different extent s. (C) 1998 Academic Press.