INTEGRATION OF BACTERIOPHAGE-MX8 INTO THE MYXOCOCCUS-XANTHUS CHROMOSOME CAUSES A STRUCTURAL ALTERATION AT THE C-TERMINAL REGION OF THE INTPPROTEIN

Mx8 is a generalized transducing phage that infects Myxococcus xanthus cells, This phage is lysogenized in M. xanthus cells by the integrati on of its DNA into the host chromosome through site-specific recombina tion. Here, we characterize the mechanism of Mx8 integration into the M. xanthus chromosome, The Mx8 attachment site, attP, the M. xanthus c hromosome attachment site, attB, and two phage-host junctions, attL, a nd attR, were cloned and sequenced, Sequence alignments of attP, attB, attL, and attR sites revealed a 29-bp segment that is absolutely cons erved in all four sequences, The intP gene of Mx8 was found to encode a basic protein that has 533 amino acids and that carries two domains conserved in site-specific recombinases of the integrase family, Surpr isingly, the attP site was located within the coding sequence of the i ntP gene, Hence, the integration of Mx8 into the M. xanthus chromosome results in the conversion of the intP gene to a new gene designated i ntR. As a result of this conversion, the 112-residue C-terminal sequen ce of the intP protein is replaced dth a 13-residue sequence, A 3-base deletion within the C-terminal region had no effect on Mx8 integratio n into the chromosome, while a frameshift mutation with the addition o f 1 base at the same site blocked integration activity. This result in dicates that the C-terminal region is required for the enzymatic funct ion of the intP product.