Genetic recombination between multiple markers of bacteriophage T4. III. A mutation which blocks a structural change...

T4 phage mutation MCO5 is a non-lethal recessive mutation which blocks recombination between multiple closely linked markers and links to genes 24 and 25. The three-factor cross, which required double exchange flanking the central marker for the formation of wild type recombinant, was blocked by MCO5 mutation. The blockage was restored by the UV irradiation of the parental phage carrying single mutation but not by the UV irradiation of the parental phage carrying double mutation. The MCO5 mutant reduced the rescue of the markers of UV-irradiated phage, although it had normal levels of sensitivity to UV in both single and multiple infections. From these results, it is concluded that MCO5 mutation blocks a structural change of DNA which is necessary for receiving DNA segment.