Mechanisms of Mitotic Recombination

Abstract

INTRODUCTION
Chromosomal recombination in Saccharomyces cerevisiae occurs at three distinct life-cycle stages of diploid cells: (1) mitotic recombination, during vegetative cell division; (2) meiototic recombination, in diploid cells uncommitted to haploidization following exposure to a meiosis-inducing environment (see Esposito and Esposito 1978); and (3) meiotic recombination, in cells that complete meiosis and ascosporogenesis (see Fogel et al. 1979). Interest in the mechanisms of mitotic recombination has been stimulated by the observation that certain mutagenic carcinogens are also recombinagens in in yeast (Zimmermann et al. 1966) and data indicating that genetic recombination is sometimes involved in the control of gene expression in prokaryotes and eukaryotes (cf. McClintock 1961; Esposito and Esposito 1977; Silverman et al. 1979). Current studies of the molecular mechanisms and genic control of spontaneous and induced mitotic recombination in S. cerevisiae focus upon answering three basic, related questions regarding mitotic exchange: (1) At what stages of the mitotic cell cycle does mitotic exchange occur? (2) Can the properties of mitotic and meiotic recombination be accounted for by a single molecular model of DNA recombination? (3) To what extent do genes controlling mitotic exchange participate in the control of meiotic recombination, homothallic interconversion of mating-type alleles, and other cellular pathways of DNA synthesis and repair? In the following discussion we summarize the properties of intergenic and intragenic mitotic recombination of standard marker loci, aspects of mitotic exchange between sister chromatids, and the phenotypes of rec mutants relevant to these questions.

MITOTIC GENE CONVERSION AND RECIPROCAL EXCHANGE
Intergenic and intragenic...