Abstract
Bacteriophage 80α is a representative of a class of temperate phages that infect Staphylococcus aureus and other Gram-positive bacteria. Many of these phages carry genes encoding toxins and other virulence factors. This phage, 80α, is also involved in high-frequency mobilization of S. aureus pathogenicity islands (SaPIs), mobile genetic elements that carry virulence factor genes. Bacteriophage 80α encodes a minor capsid protein, gp44, between the genes for the portal protein and major capsid protein. Gp44 is essential for a productive infection by 80α but not for transduction of SaPIs or plasmids. We previously demonstrated that gp44 is an ejection protein that acts to promote progression to the lytic cycle upon infection and suggested that the protein might act as an anti-repressor of CI in the lytic–lysogenic switch. However, an 80α Δ44 mutant also exhibited a reduced rate of lysogeny. Here, we show that gp44 is a non-specific DNA binding protein with affinity for the blunt ends of linear DNA. Our data suggest a model in which gp44 promotes circularization of the genome after injection into the host cell, a key initial step both for lytic growth and for the establishment of lysogeny.
Highlights
Staphylococcus aureus is a Gram-positive bacterium and an opportunistic human pathogen responsible for a broad range of diseases [1]
Bacteriophage 80α (GenBank ID: DQ517338) is a representative of a class of temperate phages that infect S. aureus and other Gram-positive bacteria [5]. Many phages in this group carry genes encoding superantigen toxins and other virulence factors [3,6,7]. 80α is involved in high-frequency mobilization of S. aureus pathogenicity islands (SaPIs), mobile genetic elements that carry genes encoding virulence factors [8]
DNA fragments corresponding to the 163 base pair cI–cro intergenic region (IGR DNA), a 1136 base pair region including the entire cI through cro genes, and a 1018 base pair sequence derived from the fibU (ORF68) tail fiber gene (TF DNA) were produced by PCR from 80α genomic
Summary
Staphylococcus aureus is a Gram-positive bacterium and an opportunistic human pathogen responsible for a broad range of diseases [1]. Bacteriophage 80α (GenBank ID: DQ517338) is a representative of a class of temperate phages that infect S. aureus and other Gram-positive bacteria [5] Many phages in this group carry genes encoding superantigen toxins and other virulence factors [3,6,7]. SOS induction and depression of the CI immunity repressor Based on these results, we hypothesized that gp was involved in the lytic/lysogenic decision, either by interfering with CI binding to its operator sequence, or by inhibiting production of the CI protein [11]. Our data are consistent with a model in which gp promotes circularization of the genome after injection into the host, a necessary initial step both for a productive lytic infection and for the establishment of lysogeny
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