Figure 6.

Competition binding analysis of MRP RNA–protein interactions. Protein complexes with ³²P-MRP RNA were challenged with increasing concentrations of unlabelled competitor RNA as indicated and the percentage of retained radiolabelled complex recorded. In general, protein subunits did not display clear specificity for MRP RNA. Data are shown for a subset of the protein–MRP RNA interactions; Pop5p, Pop4p, Snm1p and Pop3p. The Pop5p and Pop3p data clearly show no evidence of a specific interaction since the MRP RNA is competed at similar rates by non-specific poly(U) and potentially specific RNAs (MRP and P RNA). Pop4p data lacks clarity with respect to specificity. MRP appears to compete a little more effectively (∼3-fold) than poly(U). Competition by P RNA is complex, appearing to transiently enhance binding to labelled MRP-RNA prior to effectively displacing it. Uniquely, Snm1p competition binding analysis indicates a degree of specificity of Snm1p for MRP RNA, with effective displacement of labelled MRP RNA achieved at ∼5-fold lower concentrations of unlabelled MRP RNA relative to poly(U) and P RNA.