FATE OF LAMBDA DNA IN A BACTERIAL HOST DEFECTIVE IN DNA SYNTHESIS

A temperature-sensitive mutant of Escherichia coli defective in DNA synthesis is also defective in the replication of phage λ DNA at 39 °C. Since this suggests that the bacterial and lambda replication processes have the thermolabile element in common, the fate of λ DNA in the bacterium was investigated. Experiments with density-labeled phage show that if any λ DNA replication occurs it is restricted to much less than one duplication. Nevertheless, a small number of phage particles are produced, indicating that all other essential phage functions must be expressed. 3H-labeled λ DNA molecules infecting the mutant are converted to covalently closed duplex molecules as efficiently as they are in the wild type. However, molecules containing parental label which sediment faster than DNA from phage particles but slower than closed duplexes are not formed in the mutant as they are in the wild type. When λ development is induced in mutant cells lysogenic for λ, the production of phage is restricted at high temperature but the prophage appears to detach from the chromosome normally. © 1969.