Conserved nucleotide sequences in temporally controlled bacteriophage promoters

Abstract

Gene expression at a middle time in the lytic cycle of Bacillus subtilis bacteriophage SP01 is controlled by the product of phage gene 28 (gp28). gp28 is a sigma-like regulatory protein that directs the bacterial core RNA polymerase to bind and initiate transcription from promoter sites for phage middle genes. Here we report on the location, orientation and nucleotide sequences of five promoters in a cluster of middle genes on the phage genome. (The nucleotide sequences of two of these promoters were reported previously by Talkington & Pero, 1979). All five promoters shared highly conserved nucleotide sequences that were centered at about 35 and 10 base-pairs upstream from their start points of transcription. Based on these conserved sequences we propose that RNA polymerase containing gp28 recognizes the prototype sequence 5′ T- -T-AGGAGA- -A- TT in the −35 promoter region and the sequence 5′ TTT-TTT in the −10 region. (In SP01 DNA, T is the thymine analog 5-hydroxymethyluracil.) These prototype sequences differ strikingly from the corresponding conserved regions of SP01 early gene promoters which are recognized by the unmodified B. subtilis RNA polymerase and which are highly homologous to promoters for Excherichia coli RNA polymerase. These findings suggest that sigma factors (host sigma and gp28) dictate the recognition of both the −35 and −10 regions of promoters.