MEPS parameters and graph analysis for the use of recombination to construct ordered sets of overlapping clones.

Homologous recombination can provide a basis for the construction of an ordered set of overlapping clones. The principle is to make two libraries, each in a vector that has a different selectable marker flanking the insert site. Recombination between the flanking markers, leading to a selectable phenotype, can only occur as the consequence of crossing over between inserts. The two libraries are crossed in a matrix, allowing the construction of an ordered set. The logic, akin to S. Benzer's (1961, Genetics 47:403-415) for the arrangement of deletion and point mutations, has a graph theoretic formulation, which helps to cope with the complex and noisy data inherent in the physical mapping of genomes rich in repeated sequences. The minimum length of identity required for homologous recombination is called the MEPS (minimum efficient processing segment) and is a property of each recombination pathway. The amount and the type of sequence similarity required for two sequences to recombine is different from that implied by either the conservation of restriction sites or by most procedures of hybridization.