Nucleoside triphosphate substrate specificity of TbTUT4. Purified TbTUT4 (50 nM), 5∼-labeled 6[U] RNA (0.2 μM) and NTPs were incubated at 27°C for 20 min. c, control – 5∼-labeled RNA primer. (a) Reactions were performed in the presence of 2 mM MgCl>2 and 0.1, 1, 10 or 100 μM NTP. (b) Reactions were performed in the presence of 2.5 mM MnCl>2 and 0.1, 1, 10, 100 or 500 μM NTP. (c) Reactions were carried out as in (a), but in the presence of 0.1, 1, 10 or 100 of μM dUTP. Products were separated on a 15% polyacrylamide/urea gel. (d) Specificity of UV-induced TbTUT4-NTP cross-linking. BSA, bovine serum albumin.