Deletion mutants of Bacillus subtilis bacteriophage SP beta.

The central portion of the chromosome of temperate Bacillus subtilis bacteriophage SPB was found to contain a region in which large deletions occurred, sometimes at high frequency. Most of the deletions could be placed into one of three groups, del1, del3, and del4, which were missing 11.8, 14.2, and 14 kilobase pairs of DNA, respectively. The chromosomal positions of the three types of deletions overlapped and together defined a continuous region of 27 kilobase pairs surrounding the prophage attachment site attPSPB. The 27-kilobase-pair segment contained no functions required for lytic growth of the phage, but DNA within this region was used as a template for RNA synthesis at several stages in the life cycle of SPB. In addition the transcription of DNA during lytic infection was found to be initiated over a large portion of one-half of the viral chromosome (the arbitrary left half). Subsequently, the synthesis of early RNA was terminated as late transcription continued on the opposite side of the chromosome.