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

Specificity of TtCutA with an excess of ATP over other nucleotides. (A) Length distribution for tails added by wild-type (WT) and mutant (PAP1 and PUP3) TtCutA_tr3 variants to ss22-A₄ (left) and ss22-U₄ (right) oligoribonucleotide substrates in the presence of 10:1:1:1 ATP:GTP:CTP:UTP molar ratio. Numbers of analyzed sequences, obtained after 3′-RACE-seq high-throughput analysis for each protein variant, are indicated in parentheses. (B,C) Analysis of nucleotide composition for tails added by different TtCutA_tr3 variants to ss22-A₄ (panel B) and ss22-U₄ (panel C) RNA substrates at physiologically relevant NTP ratio. Results are presented as in Figure 6.