Purification and Characterization of an Adenosine Triphosphate-stimulated Factor That Enhances the Nuclear Binding of Activated Glucocorticoid-receptor Complex from Rat Liver

The ATP-stimulated translocation promoter (ASTP), a protein that increases the nuclear binding of partially purified activated glucocorticoid-receptor complexes (GRC) in the presence of ATP, was purified from the liver of adrenalectomized rats to apparent homogeneity, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purification procedure consisted of DEAE-cellulose chromatography, heat treatment (60 C; 3.5 min), and sequential chromatographies on agarose gel filtration, hydroxylapatite, Mono Q, and S-Sepharose. ASTP had a mol wt of 93,000, as determined by gel filtration on Bio-Gel A-0.5 m, and was composed of two apparently identical subunits with mol wt of 48,000, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The sedimentation coefficient of ASTP was 6.5s, and its isoelectric point was 4.5. ASTP activity was dependent on the physiological concentration of ATP, although ASTP did not bind to ATP-agarose. Neither ADP nor AMP affected its activity. An analysis of the nuclear binding behavior of GRC suggested that the affinity of GRC for nuclei in the presence of ASTP is much greater than that in the absence of ASTP. In the presence of ATP, ASTP increased the binding of GRC to chromatin, but not to DNA-cellulose, suggesting that ASTP acts as a regulatory component, altering the chromosomal binding of GRC in rat liver.