A large-molecular-weight regulating factor for chromatin-dependent RNA polymerase II reactions in rat liver cytoplasm.

The author found a sugar-containing 70 KDa factor in rat liver nuclei as described in the previous report (1), which repressed RNA chain initiation by all classes of rat liver RNA polymerases and specifically stimulated chromatin-dependent RNA chain elongation catalyzed by RNA polymerase II. In this communication, the localization of this factor in rat hepatic cells was studied. In the cytoplasmic fraction, a large-molecular-weight regulating activity for chromatin-dependent RNA polymerase II reactions was observed and it was characterized to be a 250 KDa glycoprotein. This factor showed the same biological activity for chromatin-dependent RNA polymerase II reactions as that of the factor reported previously (1). Furthermore, this factor was converted to the 70 KDa factor by the action of exogenous or unknown endogenous protease(s). These results suggest that a conversion mechanism from cytoplasmic factor to nuclear factor for RNA polymerase II-dependent transcription exists.