Properties of an intermediate-sized androgen receptor: association with RNA

This study identifies an intermediate-sized androgen receptor and characterizes its relationship with the 9.1S and 4.4S receptor forms. Under low ionic conditions, at 2-4 degrees C, there exists a 9.1S (+/- 0.17) (n = 30) oligomeric form which does not bind to DNA. Under high ionic conditions, this form dissociates to a 4.4S (+/- 0.08) (n = 18) monomeric form. When the salt concentration is lowered, the 4.4S monomer converts to a species with an intermediate sedimentation coefficient of 7.7S (+/- 0.15) (n = 17) which binds to DNA. Unlike the 9.1S oligomer the 7.7S form is not maintained by sodium molybdate under high ionic conditions but rather dissociates to the 4.4S monomer. To determine whether these forms were associated with RNA, the 7.7S form was incubated with RNase A and analyzed by density gradient centrifugation. The 7.7S form was digested fully by RNase to the 4.4S monomer. The 7.7S form demonstrated a buoyant density of 1.2459 +/- 0.014 g/cm3 (n = 6) in metrizamide gradients, suggesting a ribonucleoprotein component. The sedimentation coefficient of the 9.1S form was unaffected by RNase. These data suggest that the intermediate 7.7S receptor form is composed of 4.4S monomer associated with a ribonucleoprotein molecule(s).