FIG. 2.
U1A protects AUGCN1-3C sequences downstream of the cleavage site between the two GU-rich regions. (A) 3′ end-labeled RNA. The indicated amounts of U1A were allowed to bind the RNA before partial RNase T1 digestion. Samples were treated with proteinase K before PAGE. Sites of RNase T1 digestion are labeled with position numbers according to the mouse IgM sequence with accession number V00818. The downstream footprint is labeled with a line, the positions of the two AUGCN1-3C sequences are indicated with asterisks. The protected bands are indicated with open symbols, and those used as comparison are indicated with solid symbols. Symbols relate to quantitation in panel B. (B) Quantitation of the bands marked with symbols in panel A by phosphorimager analysis. Results were normalized to zero U1A. Symbols refer to bands marked with equivalent symbols in panel A. (C) Schematic diagram of predicted RNA structure of the poly(A) site and the downstream region (position 1949 to 2085). The position of the RNase T1 cuts are indicated with arrows of the size proportional to the intensity of the cut. Positions of RNase T1 cuts quantitated in panel B are indicated with the equivalent symbol. The AUGCN1-3C motifs are indicated with brackets and labeled with asterisks. The positions of the GU-rich sequences are indicated by arrows and shaded.