Antitermination of early transcription in phage HK022. Absence of a phage-encoded antitermination factor.

In phage lambda and its relatives most early phage genes are located downstream from transcription termination sites, and full gene expression requires suppression of termination (or antitermination). Phage HK022, a lambda relative, also antiterminates early transcription, but, unlike its relatives, does so in the absence of any active phage gene product. We found no functional equivalent of the lambda N antitermination protein in HK022. In addition, nus mutations, which alter host proteins required for lambda antitermination, have no apparent effect on HK022 early gene expression. We have shown that terminators located several thousand base-pairs from the start point of transcription are suppressed, and that in the left operon suppression requires a short, promoter-proximal segment. A 40 bp region within this segment is repeated in the right operon. The chromosomal locations of these repeated segments resemble those of the nut antitermination sites of other lambdoid phages, but the HK022 sites lack the conserved sequence elements of the nut sites. It appears that HK022 antiterminates early transcription in a novel way.