Genetic control of intrachromosomal recombination

Intrachromosomal recombination between direct repeats can occur either as gene conversion events, which maintain exactly the number of repeat units, or as deletions, which reduce the number of repeat units. Gene conversions are classical recombination events that utilize the standard chromosome recombination machinery. Spontaneous deletions between direct repeats are generally recA-independent in E. coli and RAD52-independent in S. cerevisiae. This independence from the major recombination genes does not mean that deletions form through a nonrecombinational process. Deletions have been suggested to result from sister chromatid exchange at the replication fork in a recA-independent process. The same type of exchange is proposed to be RAD52-independent in Saccharomyces cerevisiae. RAD52-dependent events encompass all events that involve the initial steps of a recombination reaction, which include strand invasion to form a heteroduplex intermediate.