STRUCTURE OF A GENOME REGION OF THE LACTOBACILLUS-GASSERI TEMPERATE PHAGE PHI-ADH COVERING A REPRESSOR GENE AND COGNATE PROMOTERS

By sequencing the DNA regions which flank the intG gene encoding integ rase of the temperate Lactobacillus (Lb.) gasseri bacteriophage phi ad h, a continuous sequence of 6590 bp was established. It encompasses fi ve newly identified ORFs, of which four are located upstream, and one (orfC) downstream of intG. Proteins corresponding to the expected prod ucts of the intG upstream coding regions, orfA (33 kDa), orf2 (14 kDa) , rad (12.1 kDa), and tec (7.9 kDa), were identified by in vitro expre ssion of subcloned DNA fragments. Rad shares homology with transcripti on regulators, including SinR of Bacillus species and the repressor of phage phi 105. The gporf2 is similar to predicted products of topolog ically equivalent coding regions of the Lactococcus lactis phage TP901 -1 and the B. subtilis phage phi 105. Promoters for the divergently or iented rad and tec genes were mapped within the 435-bp region between them and specify overlapping transcripts with extended 5'-untranslated sequences. As shown with lacZ fusions, Rad repressed transcription fr om the tec and inn promoters 20- and 5-fold, respectively. In Lb. gass eri, weak expression of cloned ran was sufficient to mediate immunity towards phi adh. (C) 1998 Elsevier Science B.V.