An activator of transcription regulates phage TP901-1 late gene expression

A promoter active in the late phase of the lytic cycle of lactococcal bacte riophage TP901-1 has been identified. The promoter is tightly regulated and requires the product of the phage TP901-1 orf29 for activity. A deletion a nalysis of the late promoter region showed that a fragment as small as 99 b p contains both the promoter and the region necessary for activation by ORF 29. The transcriptional start site of the promoter was identified by primer extension to position 13073 on the TP901-1 genome, thus located 87 bp down stream of orf29 in a 580-bp intergenic region between orf29 and orf30. Furt hermore, the region located -85 to -61 bp upstream of the start site was sh own to be necessary for promoter activity. During infection, the transcript arising from the late promoter is fully induced at 40 min postinfection, a nd our results suggest that a certain level of ORF29 must he reached in ord er to activate transcription of the promoter. Several lactococcal bacteriop hages encode ORF29 homologous proteins, indicating that late transcription may be controlled by a similar mechanism in these phages. With the identifi cation of this novel regulator, our results suggest that within the P335 gr oup of lactococcal phages at least two regulatory systems controlling trans cription in the late stage of infection exist.