Temporally Regulated Transcriptional Expression of the Genomes of Lactococcal Bacteriophages c2 and sk1.

Transcription maps of the Lactococcus lactis subsp. lactis prolate phage c2 and small isometric phage sk1 were constructed. Early and late transcripts were demonstrated in phage c2. Early transcription was localized to within a 7.5-kb EcoRV fragment, and late transcription included the region which encodes the phage structural proteins and a lysin gene. Early, middle, and late transcripts were demonstrated in phage sk1. Transcription was confined to an 11.3-kb region defined by the three EcoRV restriction fragments of 6.2, 4.7, and 0.46 kb during the early part of the sk1 life cycle. Middle gene transcripts extended from the EcoRV site (defining the left-hand limit of early gene expression) through the cos site and included the 4.3-kb PvuII-cos fragment. Late transcription was detected over the remainder of the phage genome. These results indicated that gene expression was temporally regulated at the level of transcription in these two lactococcal phages and that two regions of time-dependent transcription exist in phage c2 and three in phage sk1.