Transcription Analysis of the Prolate-Headed Lactococcal Bacteriophage c2

A detailed transcription map of the prolate-headed lactococcal phage c2 has been constructed. Transcription of about one-third of the genome, encoding 22 open reading frames, began within the first 2 min of infection and produced at least 12 overlapping transcripts that persisted until lysis occurred at 30 min after initiation of infection. The remaining two-thirds of the genome, encoding 17 open reading frames, was divergently transcribed, beginning between 4 and 6 min after initiation of infection, and resulted in at least 18 overlapping transcripts that persisted until lysis. Five very strong, simultaneously active, and probably unregulated early promoters and a single positively regulated late promoter were identified. The late promoter had an extended 210 sequence, had a significant basal level of activity in the uninduced state, and was induced to high activity by a phage gene product. The complex overlapping pattern of transcripts resulted from the action of the multiple early promoters, inefficient termination of transcription, and (possibly) processing of a late precursor transcript(s). Phage proteins were not required for these processes, and the host RNA polymerase was probably used for both early and late transcription. Lactococci are used extensively as starter cultures in the production of fermented dairy products. These bacteria are often exposed to phages during the manufacturing process, which may result in the lysis of susceptible strains. Lactococcal phages are classified into 12 species (25). Most lactococcal phage species conform to one of two morphotypes: B1, a small isometric head and a long noncontractile tail; and B2, a prolate head and a long noncontractile tail. Nearly all of the small isometric phages fall into two species groups designated 936