Role of Nucleases in Genetic Recombination

Abstract

INTRODUCTION
Genetic recombination has been defined by Clark as the interaction of nucleic acids so as to produce a change in the linkage relationships between genes or parts of genes (Clark 1971). While the phenomenon has been recognized in higher organisms for nearly three-quarters of a century, the discovery of genetic recombination in bacteria and bacteriophage some 35 years ago led to considerable impetus towards the determination of the mechanisms by which it occurred.

Initial mechanisms were of the copy-choice variety (Levinthal 1954), which invoked the alternate copying of one DNA molecule and then another to produce a new, recombinant DNA structure. However, copy-choice models fell from favor with the discovery that DNA replicated by a semiconservative mechanism (Meselson and Stahl 1957) and with the density-shift experiments of Meselson and Weigle (1961) which showed that phage λ recombination involved breakage and reunion of DNA molecules. The pendulum has swung back somewhat with the realization that there is a definite correlation between recombination events and DNA replication in bacteriophages λ (Stahl 1979) and T7 (Burck and Miller 1978; Smith and Miller 1981). Furthermore, models for the movement of transposons and bacteriophage Mu (Arthur and Sherratt 1979; Shapiro 1979) also place a heavy emphasis on a role for DNA replication.

Genetic recombination can be broadly classified into two types: (1) general recombination and (2) site-specific recombination. General recombination implies that the breakage and rejoining of DNA takes place between homologous DNA molecules and that the likelihood of recombination is comparable in all...