STRUCTURE OF REC2, A RECOMBINATIONAL REPAIR GENE OF USTILAGO-MAYDIS, AND ITS FUNCTION IN HOMOLOGOUS RECOMBINATION BETWEEN PLASMID AND CHROMOSOMAL SEQUENCES

Mutation in the REC2 gene of Ustilago maydis leads to defects in DNA r epair, recombination, and meiosis. Analysis of the primary sequence of the Rec2 protein reveals a region with significant homology to bacter ial RecA protein and to the yeast recombination proteins Dmc1, Rad51, and Rad57. This homologous region in the U. maydis Rec2 protein was fo und to be functionally sensitive to mutation, lending support to the h ypothesis that Rec2 has a functional RecA-like domain essential for ac tivity in recombination and repair. Homologous recombination between p lasmid and chromosomal DNA sequences is reduced substantially in the r ec2 mutant following transformation. The frequency can be restored to a level approaching, but not exceeding, that observed in the wild type strain if transformation is performed with cells containing multiple copies of REC2.