GENETIC-DETERMINANTS OF IMMUNITY AND INTEGRATION OF TEMPERATURE MYXOCOCCUS-XANTHUS PHAGE MX8

An 8.1-kb fragment of the temperate Myxococcus xanthus phage Mx8 genom e, when cloned into a plasmid vector, permits site-specific integratio n of the plasmid and confers superinfection immunity. Sequence analysi s of a 9.5-kb region of Mx8 DNA containing this fragment reveals 19 de nsely pack;ed open reading frames, four of which have predicted produc ts with known or suspected activities. The Mx8 imm gene, required for superinfection immunity, has a sequence similar to that of Arabidopsis thaliana G-box-binding factor 1, Mx8 makes a DNA adenine methylase, M ox, and integrase, fnr, related to other methylases and integrases, Th e inf gene has two alternate translation initiation codons within the extensively overlapping uoi (upstream of int) gene, Comparison of the predicted product of the uoi gene with Salmonella phage P22 and Strept omyces plasmid Xis proteins shows that temperate phage excisionases ma y use variations of a helix-turn-helix motif to recognize specific DNA sequences.