Involvement of very short DNA tandem repeats and the influence of the RAD52 gene on the occurrence of deletions in Saccharomyces cerevisiae

Chromosomal rearrangements, such as deletions, duplications, or Ty transpos ition, are rare events. We devised a method to select for such events as Ur a(+) revertants of a particular ura2 mutant. hmong 133 Ura(+) revertants, 1 4 were identified as the result of a deletion in URA2. Of seven classes of deletions, six had very short regions of identity at their junctions (from 7 to 13 bp long). This strongly suggests a nonhomologous recombination mech anism for the formation of these deletions. The total Ura(+) reversion rate was increased 4.2-fold in a rad52 Delta strain compared to the wild type, and the deletion rate was significantly increased. All the deletions select ed in the rad52 Delta context had microhomologies at their junctions. We pr opose two mechanisms to explain the occurrence of these deletions and discu ss the role of microhomology stretches in the formation of fusion proteins.