Bacteriophage T4 gp2 interferes with cell viability and with bacteriophagelambda red recombination

The T4 head protein, gp2, promotes head-tail joining during phage morphogen esis and is also incorporated into the phage head. It protects the injected DNA from degradation by exonuclease V during the subsequent infection. Ln this study, we show that recombinant gp2, a very basic protein, rapidly kil ls the cells in which it is expressed. To further illustrate the protective ness of gp2 for DNA termini, we compare the effect of gp2 expression on Red -mediated and Int-mediated recombination, Red-mediated recombination is non specific and requires the transient formation of double-stranded DNA termin i, Int-mediated recombination, on the other hand is site specific and does not require chromosomal termini, Red-mediated recombination is inhibited to a much greater extent than is Int-mediated recombination, We conclude from the results of these physiological and genetic experiments that T4 gp2 exp ression, like Mn Gam expression, kills bacteria by binding tu double-strand ed DNA termini, the most likely mode for its protection of entering phage D NA from exonuclease V.