Biochemical and structural bioinformatics studies of fungal CutA nucleotidyltransferases explain their unusual specificity toward CTP and increased tendency for cytidine incorporation at the 3′-terminal positions of synthesized tails

Different affinity of TtCutA_tr3 variants toward individual NTPs. (A–C) Nucleotidyltransferase activity assays were performed for WT, PAP1, and PUP3 TtCutA_tr3 protein variants, with 40-fold molar excess of the 5′-FAM-labeled ss22-A₄ RNA substrate. Reactions were programmed with individual ATP (A), CTP (B), or UTP (C) at different concentrations, as indicated above the lanes and terminated after short time points (2–12 min) following start of incubation.