CF Im subunits coimmunoprecipitate with snRNPs. (A) The snRNP-containing heavy fractions were immunoprecipitated with mAb 2.73, mAb 1E1, Y12, and mAb 12E12. The first lane (light) is the light fraction immunoprecipitated with mAb 2.73 for visualization of the 72-, 68-, and 59-kD CF Im subunits (the amount of light fraction precipitated was one-fourth of that used for the heavy fraction precipitation). The precipitated proteins were separated by 10% SDS-PAGE and subjected to Western analysis probing with antibody against the 68-kD subunit of CF-Im (top panel) or antibody against U1A protein (bottom panel). (B) In vitro synthesized, [35-S]-met-labeled 68- and 25-kD subunits were incubated with nuclear extract. The total snRNP fraction was isolated using affinity chromatography (see text and Materials and Methods), equivalent proportions of the depleted nuclear extract and purified snRNPs were separated by 10% SDS PAGE, and the gel dried and autoradiographed. Positions of significant proteins and the immunoglobulin heavy chain (hc) are indicated.
