Fig. 4. SXL associates with the U1 snRNP particle in embryonic extracts. (A) The SXL/U1-70K association is more robust than the SXL/SNF association. The ability of SXL to associate with SNF and U1-70K in whole cell extracts was tested by GST pull-down assays, followed by western blotting. The RNase sensitivity of these interactions was tested by pre-treating the embryonic extracts with a combination of RNaseA and RNase T1. (B) SXL associates with U1-70K in snf¹⁴⁸ mutant extracts. GST pull-down experiments were carried out as in Fig. 2, with extracts made from wild-type and a homogenous population of embryos whose only source of SNF protein is the mutant SNF¹⁴⁸ protein.