The regulation of nuclear DNA template restrictions by acidic polymers

As presented in the Introduction it is now apparent that in heterokaryon cells cytoplasmic factors are capable of interacting with mammalian nuclei and inducing nucleic acid synthesis. These nucleocytoplasmic interactions are accompanied by a marked increase in nuclear volume, dispersion of chromatin and increase in nuclear DNA template function. To our knowledge the only factors which are capable of mimicking all of these cellular effects on isolated nuclei are specific large acidic polymers such as acidic proteins, acidic polysaccharides and ribonucleic acids. We have initiated a detailed study of the interactions of various types of acidic polymers on isolated nuclei and chromatin and our observations have formed the basis for this review. The regulation of DNA synthesis in mammalian cells may be a complex process involving multiple enzyme systems and initiating factors (see reviews by Simpson (1), Stein and Baserga (66) and Barlow (115)). Many of these regulatory processes require specific events at various phases of the cell cycle (65). Increasing attention has been focused on the possible role of nuclear acidic proteins as one of the important factors in regulating nucleic acid synthesis in the cell (66). The models which we have proposed in our studies may provide new insight into this problem.