ISOLATION OF MULTIPLE ACTIVITIES FROM MOUSE FM3A CELLS WHICH PROMOTE HOMOLOGOUS PAIRING OF DNA-MOLECULES

We describe the detection and partial purification of three homologous pairing activities from extracts of mouse mammary carcinoma FM3A cell s. These activities, designated MHP1a, 1b, and 1c, form joint molecule s between circular single-stranded DNA and homologous linear duplex DN A and are distinguished from one another by their chromatographic beha viors or isoelectric properties. The reactions promoted by these activ ities require homologous substrates but not ATP. All the reactions als o show Mg2+ dependence in the absence of exogenous ATP. Analysis of th e reaction products has revealed that strand exchange proceeds for len gths of up to at least 2,71 bp during the homologous pairing reaction. The finding of multiple types of homologous pairing and strand exchan ge activity in mouse cells may facilitate the elucidation of the mecha nism of homologous recombination in somatic mammalian cells.