A 35-kDa protein binding to a cytosine-rich strand of hypervariable minisatellite DNA

A minisatellite-binding protein, Msbp-4, with a molecular mass of 35 kDa has been purified from mouse tumor cells that binds to hypervariable Pc-1 and Pc-2 minisatellites. The binding is much more efficient than that to genetically stable minisatellite homologues. As assayed by Southwestern analysis, Msbp-4 favors multiple copies of the Pc-2 repeat sequence GGCAGGA and requires the cytosine-rich single strand for the binding. The activity is also present in extracts from mouse testis but not from liver. The phosphatase treatment revealed that Msbp-4 is phosphorylated and may have a regulatory function, because dephosphorylation affects the activity and specificity of the binding. Sequence preference is demonstrated by a competition experiment using single-base substitution mutants. Thus, the binding properties of Msbp-4 observed here lead to an implication that the protein-DNA complexes result in formation of a single-stranded DNA loop of the G-rich strand in the minisatellite which may enhance the ability of the minisatellite to undergo recombination.