The effect of 5-bromodeoxyuridine on the synthesis of nuclear and cytoplasmic DNA-binding proteins isolated from sea urchin embryos.

Newly synthesized DNA-binding proteins were isolated from the nuclei and, separately from, the cytoplasm of sea urchin mofula stage embryos. The presence of 5-bromodeoxyuridine during embryogenesis did not appear to alter the synthesis of either class of DNA-binding proteins. This result tends to argue that cell differentiation in early embryos is not regulated by differential synthesis of DNA-binding proteins. Sea urchin mofulae synthesize a broad range, by molecular weight, or cytoplasmic DNA-binding proteins which dissociate from sea urchin DNA-cellulose at relatively high salt concentrations (0.6-2.0 M NaCl). The most prominant of these apparently high-binding-affinity proteins has an approximate molecular weight of 33,000.