GENETIC-RECOMBINATION OF NUCLEOSOMAL TEMPLATES IS MEDIATED BY TRANSCRIPTION

An in vitro system has been developed to examine the influence of tran scription on genetic rearrangement. Using a homologous pairing assay, the transfer of one strand of a nucleosomal template onto a recipient DNA molecule was monitored as a function of RNA polymerase activity. T ranscriptionally inactive nucleosomal DNA was refractory to homologous pairing. Homologous pairing was catalyzed, however, by the eukaryotic recombinase, reel, when the nucleosomal template was being transcribe d. The reaction was found to be dependent on the presence of reel, RNA polymerase, NTPs and RNA synthesis. Heteroduplex formation between a short DNA duplex fragment assembled into a nucleosome and a single-str anded circle relied also on the presence of sequence homology between the duplex and the circle. The results of this study lend support to t he notion that transcriptionally active regions within a chromosome ar e more apt to serve as sites of genetic recombination.