Fig. 5. SAFB2 protein is a component of higher molecular mass nuclear complexes, which contain a core set of protein interaction partners. Nuclear extracts were fractionated either (A) directly on a sucrose gradient, or (B) after pre-treatment with micrococcal nuclease to remove endogenous RNA. Fraction 20 was from the top of the gradient, and fraction 1 from the bottom. The pelleted material is in lane P. The migration of individual proteins was monitored by SDS-PAGE and immunoblotting. The mobility of size markers on the gradients is shown. (C,D) Both -SAFB1 and -SAFB2 efficiently immunoprecipitate their cognate proteins, and SAFB1 and SAFB2 proteins reciprocally co-immunoprecipitate each other. (E-H) Antisera to both proteins also co-immunoprecipitate (E) Sam68 and (F) hnRNP G. No co-immunoprecipitation was observed with (G) PRP19, or (H) the large subunit of RNA polymerase II containing the carboxyl-terminal domain (CTD).