Interaction of rat liver glucocorticoid receptor with histones

The activated glucocorticoid-receptor complexes (GRC) from rat liver bind tightly to histone (from calf thymus)-agarose and cannot be eluted with 3 M KCl or 50% ethylene glycol, but can be eluted with 20 mM pyridoxal 5'-phosphate (PALP). Purified activated GRC were found to have much higher affinity for histones H3 and H4 (arginine-rich histones) than for histones H2A and H2B (slightly lysine-rich histones) and to have negligible affinity for histone H1 (lysine-rich histone). The GRC bound to immobilized histones could be eluted with PALP, but not with its related compounds, such as pyridoxamine, pyridoxamine 5'-phosphate, pyridoxal, and pyridoxine, suggesting a specific effect of PALP. Not only activated GRC but also unactivated GRC were found to bind to immobilized histones. However, from their profiles of elution from a histone-agarose column by 20 mM PALP, the activated GRC seemed to have higher affinity than unactivated GRC for histone. Our results suggest that the binding of GRC to histones could be associated with a mechanism for alteration of the chromosome structure by the hormonal signals, before the binding of the GRC to a specific sequence of DNA in regulatory elements of glucocorticoid-responsible genes.