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J. Bacteriol., 02 1996, 1099-1104, Vol 178, No. 4
C Schmidt, M Velleman and W Arber
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 444 bp in length, respectively, with the stop
codon of lydA overlapping the start codon of lydB. The third, gene 17, is
558 bp in length and is located in an otherwise uncharacterized operon. A
search with the predicted amino acid sequence of LydA for secondary motifs
revealed a holin protein-like structure. Comparison of the deduced amino
acid sequence of gene 17 with sequences of proteins in the SwissProt
database revealed homologies with the proteins of the T4 lysozyme family.
The sequence of lydB is novel and exhibited no known extended homology. To
study the effect of gp17, LydA, and 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 harboring pAW1442. In contrast, cells harboring
pAW1440 revealed only a small decrease in optical density at 600 nm
compared with cells harboring vector alone. The rapid lysis phenotype in
the absence of active LydB suggests that this novel protein might be an
antagonist of the holin LydA.
Copyright © 1996, American Society for Microbiology
Three functions of bacteriophage P1 involved in cell lysis
Abteilung Mikrobiologie, Biozentrum Universitat Basel, Switzerland.
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