Duplication of the bacteriophage lambda cohesive end site: genetic studies

A derivative of bacteriophage λ has been isolated that contains a duplication of the cohesive end site. To support this conclusion, the duplicated region has bean recovered by segregation from a lysogen of the duplication strain, and a derivative of the duplication strain was constructed that is heterozygous for the λ genes R and A, which bracket the cohesive end site. Duplication strains show no instability during lysogenization, suggesting that the virus particles each contain a single DNA molecule. During lytic growth, however, the strain is unstable and the duplication is frequently lost, even in the absence of all known recombination systems. Loss of the duplication is ascribed to cleavage of both cohesive end sites by the chromosome maturation system. Thus both cohesive end sites are functional, i.e. capable of being cleaved. No transfer of the duplicated region occurs in the absence of the known recombination systems. Thus, during λ chromosome maturation, cleavage of DNA molecules occurs but rejoining of cleaved molecules does not.