3 FUNCTIONS OF BACTERIOPHAGE-P1 INVOLVED IN CELL-LYSIS

Amber and deletion mutants were used to assign functions in cell lysis to three late genes of bacteriophage p1. Two of these genes, lydA and lydB of the dar operon, are 330 and 434 bp in length, respectively, w ith the stop codon of lydA overlapping the start codon of lydB. The th ird, gene 17, is 558 bp in length and is located in an otherwise uncha racterized operon, A search with the predicted amino acid sequence of LydA for secondary motifs revealed a holin protein-like structure, Com parison of the deduced amino acid sequence of gene 17 with sequences o f proteins in the SwissProt database revealed homologies with the prot eins of the T4 lysozyme family, The sequence of lydB is novel and exhi bited no known extended homology, To study the effect of gp17, LydA, a nd LydB in vivo, their genes were cloned in a single operon under the control of the inducible T7 promoter, resulting in plasmid pAW1440. A second plasmid, pAW1442, is identical to pAW1440 but has lydB deleted, Induction of the T7 promoter resulted in a rapid lysis of cells harbo ring: pAW1442, In contrast, cells harboring pAW1440 revealed only a sm all decrease in optical density at 600 nm compared with cells harborin g vector alone. The rapid lysis phenotype in the absence of active Lyd B suggests that this novel protein might be an antagonist of the holin LydA.