Partial purification and characterization of two types of homologous DNA pairing activity from rat testis nuclei.

We describe the partial purification and characterization of two different types of homologous DNA pairing activity from rat testis nuclear extracts. The activities are separated from each other by single-stranded DNA-cellulose affinity chromatography. One activity requires single-stranded DNA ends and promotes the homologous pairing of single-stranded DNA fragments with double-stranded circular DNA and has an apparent molecular mass of 100 kDa as determined by gel filtration chromatography. This pairing activity does not require the addition of exogenous ATP and is strongly Mg2+ -dependent. The second pairing activity promotes strand-transfer between single-stranded circular DNA and homologous double-stranded DNA fragments and has an apparent molecular mass of 30 kDa as determined by gel filtration chromatography. This pairing activity also does not require ATP but, in contrast to the former, is Mg2+ -independent.