Phosphorylation affects the DNA affinity of the nuclear protein 24/7 from human tumor cells

In the present study we investigated the binding behavior of nuclear proteins from human tumor cells to human placental DNA coupled on CNBr-activated Sepharose. When nuclear proteins soluble in 5 M urea prepared from serum-stimulated cells and containing the majority of the nonhistone proteins were applied onto a dsDNA column, next to several other proteins one prominent group consisting of at least 2 distinct proteins with a pI at 7 and a molecular mass near 24 kDa bound to DNA. The DNA-binding ability of one of them is lost on phosphorylation and is recovered after dephosphorylation using alkaline phosphatase. Additionally, normal human fibroblasts taken as controls exhibit comparatively low levels of these 24/7 proteins, indicating a particular function in tumor cells.