A low-molecular-weight translocation modulator and its interaction with a macromolecular translocation inhibitor of...

When rat liver cytoplasm free of glucocorticoid receptors was dialyzed, its inhibitory effect on nuclear uptake or binding of already "activated" receptor-glucocorticoid complex increased. A macromolecular fraction and a low-molecular-weight fraction separated from the cytoplasm by gel filtration both inhibited nuclear uptake or binding of the activated complex. The macromolecular fraction was much more inhibitory than the low-molecular-weight fraction. When the two components were mixed, their inhibitory effects decreased. These results suggest that, in addition to the macromolecular translocation inhibitor(s) known to be present in rat liver cytoplasm, there is a low-molecular-weight factor(s) which is also involved in the process of translocation of the activated receptor-glucocorticoid complex to the nucleus. The mechanism of action of this modulator is unknown, but its inhibitory effect seems to be due to its direct interaction with the activated receptor-steroid complex.