Isolation of SH-containing DNA-nucleoproteins by chromatography on organomercurial polysaccharide

Abstract

1.1. The nuclear proteins of rat-liver have been fractionated on organomercurial polysaccharide, a new material for the separation and isolation of sulphhydryl-containing proteins on columns.2.2. The total nuclear proteins of rat-liver (nuclear sonicate) were separated into four fractions according to increasing sulphydryl content. The fractions contained 20, 45, 65 and 230 μmoles of -SH per g of protein. The latter thiol-rich fraction was not present in an extract (1 M NaCl) of the nuclei.3.3. Some (20%) of the total DNA of the nuclear sonicate appeared in the nonadsorbed fraction, whereas the remaining 80% of the DNA was bound rather firmly to the column.4.4. Evidence is presented that the latter type of DNA, which was isolated by elution with ammonium salts of EDTA, was associated with proteins containing reactive, readily accessible SH groups.5.5. About 15% of the titratable SH-groups on the DNA-nucleoproteins were sufficiently reactive to form mixed disulphides with the radioprotective agents cystamine and cysteamine.6.6. The possible sifnificance of the nucleoprotein SH-groups in radioprotection and in cell-division are discussed.