A PHAGE-T4 SITE-SPECIFIC ENDONUCLEASE, SEGE, IS RESPONSIBLE FOR A NONRECIPROCAL GENETIC EXCHANGE BETWEEN T-EVEN-RELATED PHAGES

The bacteriophage T4 scgE gene encoding site-specific endonuclease lie s between the hoc.1 and uvsW genes. The similar region of T-even-relat ed phage RB30 lacks the segE gene, Here me demonstrate that the phage T4 segE gene is inherited preferably by progeny of mixed infection wit h RB30, The preferred inheritance of the segE gene depends on its own expression and is based on a non-reciprocal homologous recombination e vent providing the transfer of the gene from the segE-containing to th e segE-lacking allele, The SegE endonuclease cleaves DNA in a site loc ated at the 5' end of the uvsW gene in the RB30 genome, The T4 DNA is also cleaved by the enzyme, but less efficiently, The cleavage at the RB30 site appears to initiate the observed conversion, which is stimul ated by DNA homology and accompanied by co-conversion of flanking mark ers, Our findings provide a novel example of endonuclease-dependent ge neration of genetic variation in prokaryotes. (C) 1997 Federation of E uropean Biochemical Societies.