Transcription activates RecA-promoted homologous pairing of nucleosomal DNA.

RecA protein catalyzes the homologous pairing of a single-stranded circular DNA and a linear duplex DNA molecule. When the duplex is packaged into chromatin, formation of homologously paired complexes is blocked. We have established a system for studying the RecA-promoted reaction by using a duplex fragment containing a single-phased nucleosome. Under these conditions there is no reaction leading to formation of joint molecule complexes. However, transcription on the chromatin template activates the formation of complexes. Reaction is dependent on RNA synthesis and DNA sequence homology and proceeds regardless of the direction of transcription.