FIG. 1.

(A) Topology of class I, II, and III holins (35, 38). (B) Features of plasmid and phage constructs. All plasmids used for inductions are based on the structure of pS105 (14) (upper structure), with the λ late promoter and the promoter-proximal genes of the late transcriptional unit (lower structure), except that in the plasmid pT4T, the S gene in the λ SRRzRz1 lysis cassette of pER157 (30) is replaced by the phage T4 t gene. In plasmid pT4TRI, the rI gene is inserted 13 nucleotides downstream of the Rz gene of pT4T. “X” designates areas where homologous recombination can occur for generation of λt recombinants.