Sam68 associates with selected polyadenylated mRNAs in mouse spermatocytes. (A) RNP capture assay using oligo (dT)–cellulose beads and pachytene spermatocyte extracts in the presence or absence of RNase A. Proteins bound to the beads were analyzed by Western blotting with the anti-Sam68 antibody. (B) The same samples were separated by SDS-PAGE and detected by Silver staining. Molecular weight markers were loaded in the first lane. Silver staining of the gel shows that, although the pattern of bands changes, several proteins were bound to the oligo (dT) beads either in the absence or presence of RNase treatment, and that overall degradation of the sample did not occur under these conditions. (C) RNP capture assay of pachytene spermatocyte extracts were performed using oligo (dT)–cellulose beads left untreated (Ctrl) or pre-absorbed for 15 min with excess synthetic polyA or polyC RNA. Proteins bound to the beads were analyzed by Western blotting with the anti-Sam68 and the anti-PABP1 antibodies. (D) RT-PCR analysis of the enrichment in target mRNAs after coimmunoprecipitation with Sam68 from isolated wild-type germ cells. Two mRNAs that resulted in unchanged Sam68^−/− testis, Gapdh and Muc3, were used as negative controls in the same experiment. (E) Western blot analysis of the quality of the control and anti-Sam68 (α-Sam68) immunoprecipitation experiments used for the RT-PCR analysis illustrated in D.