The N-acetylmuramoyl-L-alanine amidase encoded by the Bacillus subtilis 168 prophage SP beta.

Heat shock of Bacillus subtilis CU1147, a strain lysogenic for SP beta c2, a prophage with a thermosensitive repressor, results in phage induction and subsequent cell lysis. Cloning in Escherichia coli and sequencing of a DNA fragment of prophage SP beta led to the identification of blyA, the gene encoding a 367 amino acid polypeptide with a molecular mass of 39.6 kDa. Purified BlyA obtained from the E. coli clone exhibited an N-acetylmuramoyl-L-alanine amidase activity. Insertional mutagenesis confirmed that the latter enzyme was associated with SP beta-phage-mediated cell lysis. Analysis of the neighbouring sequence suggested that the two ORFs immediately downstream of blyA and belonging to the same operon encode polypeptides which may be involved in the release of the endolysin. The presence on the chromosomes of B. subtilis or related Bacillus spp. of other, similar genes, and their possible relationship, is discussed.