Nucleotide sequence and mutational analysis of an immunity repressor gene from Bacillus subtilis temperate phage ?105

摘要

We have identified and sequenced a bacteriophage ?105 gene encoding an immunity repressor, the first to be characterized from a temperate phage infecting a Gram-positive host. Using superinfection immunity as an assay for repressor function, the ?105 repressor gene was located within a 740-bpPvuII-HindIII subfragment near the left end of the ?105 EcoRI-F fragment. We show that the repressor is specified by the 5′-proximal coding sequence of a translationally overlapping gene pair, transcribed from right to left on the conventional ?105 map. Comparison of its amino acid sequence (146 residues) with that of a large number of Gram-negative bacterial and phage repressors revealed a putative DNA-binding region between positions 20 and 39. The coding region is preceded by a strong Shine-Dalgarno sequence 5′AAAGGAG 3′. Deletion analysis of the 5′-flanking DNA allowed to identify transcriptional control elements. Their structure, 5′ TTGTAT 3′ at-35 and 5′ TATAAT 3′ at -10, strongly suggests that the ?105 repressor gene is transcribed by the major vegetative form of B. subtilis RNA polymerase, as would be expected for an early phage gene.