GENE-XV OF BACTERIOPHAGE-PRD1 ENCODES A LYTIC ENZYME WITH MURAMIDASE ACTIVITY

Bacteriophage PRD1 is a lipid-containing virus that infects a variety of Gram-negative bacteria, including Escherichia coli. The phage lyses its host by virtue of a virally-encoded lytic enzyme, the synthesis o f which has been assigned to gene XV on the basis of complementation a nalysis and experiments with mutant phages. We report here the cloning of gene XV into an expression plasmid and the purification of its pro duct, protein P15, to near homogeneity. The purified protein P15, iden tified by N-terminal sequence analysis, showed a strong lytic activity against chloroform-treated Gram-negative cells. No activity against G ram-positive bacterial species could be detected. The pH optimum of th e enzyme was between 7.0-8.0. Protein P15 was readily inactivated at t emperatures above 4 degrees C, as well as by increasing the ionic stre ngth of the buffers. The analysis of cell wall digests indicated that P15 is a glycosidase that cleaves the beta(1-4) linkage between N-acet ylmuramic acid and N-acetylglucosamine, thus displaying muramidase act ivity.