Protein binding to c-src 78-mer 5′ RNA. top: PTB1 + 78-mer 5′ RNA. Stoichiometry experiment at 1 µM RNA ♦ 39-mer 5′ RNA. ○ 78-mer 5′ + N1 RNA. 100 mM NaCl, 10 mM sodium cacodylate pH 7.5, 1 mM MgCl2, 10 mM DTT, 22° C. EMSA with PTB1 and 78-mer 5′ RNA. bottom: EMSA of PTB1:12 and PTB1:34 + 78-mer 5′ RNA. Gel mobility shift experiments at 4° C in 100 mM NaCl, 10 mM sodium cacodylate pH 7.5, 1 mM MgCl2, 10 mM DTT, 10 µg/mL tRNA, 20 µg/mL BSA.