MICROCONVERSION BETWEEN MURINE H-2 GENES INTEGRATED INTO YEAST

PATCHWORK homology observed between divergent members of polymorphic multigene families is thought to reflect evolution by short-tract gene conversion (nonreciprocal recombination), although this mechanism cannot usually be confirmed in higher organisms1-12. In contrast to meiotic conversions observed in laboratory yeast strains, apparent conversions between polymor-phic sequences, such as the class I loci of the major histocompatibil-ity complex (MHC), are short and do not seem to be associated with reciprocal recombination (crossover, exchanges)7-9,13-23. We have now integrated two nonallelic murine class I genes into yeast to characterize their meiotic recombination. We found no cross-overs between the MHC genes, but short-tract 'microconversions' of 1-215 base-pairs were observed in about 6% of all meioses. Strikingly, one of these events was accompanied by a single base-pair mutation. These results underscore both the importance of meiotic gene conversion and sequence heterology in determining conversion patterns between divergent genes. © 1990 Nature Publishing Group.