A 120-kDa protein (p120) specifically binding the major mouse satellite was
detected by the gel retardation assay in liver nuclear matrix extract. The
major satellite does not have a discrete binding site for p120; rather, mu
ltiple contact regions are distributed along the whole satellite. The bindi
ng is likely to depend on the structural properties of the major satellite,
rather than on its specific nucleotide sequence. A number of p120 characte
ristics resemble those of the MAR/SAR-binding protein SAF-A. Antibodies aga
inst the major satellite-protein complexes reveal p120 in the mouse and hum
an nuclear matrix. Immunofluorescence staining shows that p120 is mainly lo
calized in the heterochromatin region and is probably involved in the forma
tion of its structure.