ABSTRACT
Holin proteins are phage-induced integral membrane proteins which regulate the access of lytic enzymes to host cell peptidoglycan at the time of release of progeny viruses by host cell lysis. We describe the identification of the membrane-containing phage PRD1 holin gene (gene XXXV). The PRD1 holin protein (P35, 12.8 kDa) acts similarly to its functional counterpart from phage lambda (gene S), and the defect in PRD1 gene XXXV can be corrected by the presence of gene S of lambda. Several nonsense, missense, and insertion mutations in PRD1 gene XXXV were analyzed. These studies support the overall conclusion that the charged amino acids at the protein C terminus are involved in the timing of host cell lysis.
Subject(s)
Bacteriophage PRD1/genetics , Membrane Proteins/genetics , Mutation , Viral Proteins/genetics , Bacterial Outer Membrane Proteins , Bacterial Proteins , Bacteriolysis , Bacteriophage PRD1/metabolism , Bacteriophage PRD1/physiology , Base Sequence , Cloning, Molecular , DNA Mutational Analysis , Escherichia coli/physiology , Escherichia coli/virology , Lipoproteins , Membrane Proteins/chemistry , Membrane Proteins/metabolism , Molecular Sequence Data , N-Acetylmuramoyl-L-alanine Amidase , Salmonella typhimurium/physiology , Salmonella typhimurium/virology , Viral Proteins/chemistry , Viral Proteins/metabolismABSTRACT
Bacteriophage PRD1 encodes two proteins (P7 and P15) that are associated with a muralytic activity. Protein P15 is a soluble beta-1,4-N-acetylmuramidase that causes phage-induced host cell lysis. We demonstrate here that P15 is also a structural component of the PRD1 virion and that it is connected to the phage membrane. Small viral membrane proteins P20 and P22 modulate incorporation of P15 into the virion and may connect it to the phage membrane. The principal muralytic protein involved in PRD1 DNA entry seems to be the putative lytic transglycosylase protein P7, as the absence of protein P15 did not delay initiation of phage DNA replication in the virus-host system used. The incorporation of two different lytic enzymes into virions may reflect the broad host range of bacteriophage PRD1.
