Differential changes of tightly chromatin-bound RNA polymerase II in starved and cycloheximide-treated rat liver nuclei.

In order to investigate the physiological function of loosely and tightly chromatin-bound RNA polymerase II in vivo (1), the changes of these enzyme activities in cycloheximide-treated or starved rat liver nuclei were studied. Total nuclear mRNA synthesis activity in starved rats was considerably decreased, but that of cycloheximide-treated rats was not affected significantly. In starved rats, tightly bound enzyme activity was much more repressed as compared with that of loosely bound enzyme. On the other hand, cycloheximide-treated rats showed the reverse relationship. Thus, mRNA synthesis activity in hepatic nuclei seems to be dependent on the tightly bound RNA polymerase II activity. However, the difference of nuclear mRNA synthesis in both cases can not be explained by the change of chromatin-bound enzyme activity of Yu (2).