SEQUENCE-ANALYSIS OF THE LEFT END OF THE BACILLUS-SUBTILIS BACTERIOPHAGE SPP1 GENOME

The left end of the genome of Bacillus subtilis bacteriophage SPP1 is represented by EcoRI DNA fragments 12 and 1 (EcoRI-12 and EcoRI-1). A number of different deletions were identified in EcoRI-1. A detailed p hysical and genetic map of EcoRI-1 from wild-type (wt) phage and SPP1 deletion mutants was constructed. Genes encoding essential products in volved in late and early stages of phage DNA metabolism were mapped at the left and right ends of the 8.5-kb EcoRI-1, respectively. Deletion s fell within the internal 5157-bp DNA segment of EcoRI-1. The nucleot ide (nt) sequence of this region and of the endpoints of two deletions , DELTAX and DELTAL, were determined. The nt sequence of the junctions in SPP1DELTAX and SPP1DELTAL showed that, in these deletions, a segme nt of DNA between short directly repeated sequences of 10 and 13 bp, l ocated 3427 and 4562 bp apart in the wt sequence, had been eliminated. In both cases, the copy of the repeated sequence was retained in the deletion mutant, consistent with the hypothesis that the deletions ori ginated by homologous intramolecular recombination. The corresponding region in wt phage had fifteen presumptive open reading frames (orfs) and the previously identified SPP1 early promoters (PE1). The poor gro wth phenotype associated with the SPP1 deletion mutants was attributed to premature transcriptional read through from promoter(s) of the ear ly region into late operon brought into close vicinity of the late gen es due to the deletion event.