FIG. 2.

Recombinant tCid1 prefers to incorporate UMP over AMP. (A) tCid1 was incubated with a 5′-labeled (A)₁₅ primer and a 0.5 mM concentration of various nucleotides: ATP, GTP, and UTP or ATP, CTP, GTP, and UTP (A, G, U, or ALL, respectively). These reaction products were then incubated with RNase A, RNase T₁, or both, as indicated, and separated by gel electrophoresis. (B) tCid1 was incubated with 0.5 mM ATP (A), 0.5 mM UTP (U), 0.5 mM ATP and 0.05 mM UTP (AU), or 0.5 mM ATP, 0.05 mM CTP, 0.05 GTP, and 0.05 mM UTP (ALL). The DADA mutant was incubated with either 0.5 mM ATP, CTP, GTP, or UTP (A, C, G, or U, respectively).