Indirect stimulation of genetic recombination

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Abstract
Recombination between lacZ alleles in crosses of .lambda.lacZ1- .times. .lambda.lacZ2- and F- lacZ1- .times. .lambda.lacZ2- in Escherichia coli (.lambda.) can be stimulated many-fold UV irradiation of one of the .lambda.lacZ phages. Analogous stimulation was observed by coinfection of the cells by UV-irradiated .lambda. phage which carries no lac region. This indirect stimulation is not dependent on induction of the SOS system. The bacterial uvr system can effectively remove the damages on the .lambda. DNA which cause the indirect stumulation. Among a number of mutations tested, only ssb-1 caused a drastic decrease in the indirect stimulation. Indirect stumulation was caused only by using phage that had a region of homology with the recombining phage. The homologous region can be separated from the recombining region by an extended nonhomologous region (> 7.9 .times. 103 base pairs). This implies that damages to the DNA molecule, which stimulate recombination, can be located very far from the recombining region of the molecule.