JUNCTIONS BETWEEN REPETITIVE DNAS ON THE PSR CHROMOSOME OF NASONIA-VITRIPENNIS - ASSOCIATION OF PALINDROMES WITH RECOMBINATION

The Paternal-Sex-Ratio (PSR) chromosome of Nasonia vitripennis contain s several families of repetitive DNAs that show significant sequence d ivergence but share two palindromic regions. This study reports on the analysis of junctions between two of these repetitive DNA families (p sr2 and psr18). Three lambda clones that hybridized to both repeat fam ilies were isolated from PSR-genomic DNA libraries through multiple sc reenings and analyzed by Southern blots. Analysis of clones showed a r egion in which the two repeat types are interspersed, flanked by unifo rm blocks of each repeat type. PCR amplification of genomic DNA confir med the contiguous arrangement of psr2 and psr18 on PSR and identified an additional junction region between these repeats that was not pres ent in the lambda inserts. We isolated and sequenced 41 clones from th e lambda inserts and genomic PCR products containing junction sequence s. Sequence analysis showed that all transitions between psr2 and psr1 8 repeats occurred near one of the two palindromes. Based on the inher itance pattern of PSR, recombination between repeats on this chromosom e must be mitotic (rather than meiotic) in origin. The occurrence of e xchanges near the palindromes suggests that these sequences enhance re combination between repeat units. Rapid amplification of repetitive DN A may have been an important factor in the evolution of the PSR chromo some.