EFFECTS OF DNA-SEQUENCE NON-HOMOLOGY ON FORMATION OF BACTERIOPHAGE-LAMBDA RECOMBINANTS

The presence of DNA sequence non-homologies limits the parental material contribution to the genomes of unduplicated bacteriophage λ recombinants. Crosses involving closely linked markers within the lacZ region of λ plac5 have been carried out under conditions severely limiting DNA synthesis. The presence of density labels distinguishing the parental phage permits an assessment of their material contribution to the lacZ recombinant phage that emerge. When both parents harbor point mutations, the recombinants exhibit a broad range of relative parental DNA contributions, providing support for the proposal that the lacZ+ recombinants that are detected under these conditions result from mismatch repair processes acting on heterozygous sites within the long regions of heteroduplex structure present in the products of recombination. The presence of a region of non-homology, either a deletion or an insertion sequence, in one of the parents results in a limitation in the material contribution of that parent to the recombinant products. When both parents carry regions of non-homology, the relative parental contributions to recombinant products are further limited and are confined to the density range expected of the products of double-stranded breakage and joining events within the region separating the two mutational sites. These observations suggest that regions of non-homology are excluded from heteroduplex structures and provide support for a role of branch migration of a Holliday (1964) structure in the formation of the heteroduplex regions that are present in the products of recombination. © 1979.