Composition and DNA-binding properties of the nuclear matrix proteins from mammalian cell nuclei

A rapidly sedimenting DNA-protein complex was isolated from nuclear lysates in 2 M NaCl and characterized with regard to its polypeptide composition and the DNA-binding properties of the purified proteins. The complex consists of the nuclear matrix with attached DNA. Electrophoresis in SDS-polyacrylamide gels revealed two major and five minor polypeptide bands, mainly in the 60 to 75 kDa molecular weight region. The DNA-matrix complex dissociated into free DNA and proteins in the presence of 2 M NaCl and 5 M urea. The proteins could be purified by chromatography on hydroxyapatite and showed a strong tendency to reassociate at 0.15 M NaCl concentration in the absence of urea. DNA was bound to the reassociated proteins at 0.15 M NaCl concentration. Part of the DNA-protein complex was stable at 1 M NaCl concentration. The binding appeared to be random with regard to the DNA sequence.