a–f RP-HPLC analysis of IVT-RNAs. PureCap analogs TriPure_0 (a), TriPure_1 (b), TetraPure_2 (c), and TeraPure_2/m6A (d) were added to the reaction. Control mRNA using cap analogs Tri_1 (e) or Tetra_2 (f) was transcribed from a DNA template containing the A-inserted promoter. The transcript was analyzed as a crude mixture (i, black line) or after being purified by preparative HPLC (ii, blue line). Purified RNA was analyzed after deprotection by irradiating 365-nm light (iii, green line). The elution time (min) of the peak was noted nearby. A ratio (%) of capped mRNA calculated based on the peak area was listed in parentheses after the elution time. g‒i Analysis of purified mRNA used to measure the biological activities. The mRNAs were named after the cap analog used. Cap(−) means no cap analog was added. AnP means it was further treated with Antarctic phosphatase. g dPAGE analysis of the 5′ end of purified mRNA cleaved with DNAzyme 10–23 to assess its capping state. The capped ratio was calculated based on the band intensities of the capped and uncapped RNA fragments. h dPAGE analysis of purified mRNAs (25 ng each). Lane 1, Cap(−); 2, TriPure_0; 3, TriPure_1; 4, TetraPure_2; 5, TetraPure_2/m6A; 6, Tri_1; 7, Tri_1/AnP; 8, Tetra_2; 9, Tetra_2/AnP. h Removal of dsRNA from purified mRNA was confirmed by dot-blot assay using anti-dsRNA J2 antibody. 250 ng mRNAs were spotted. As a positive control of the assay, the dsRNA sample was dotted in spots 1 to 5 (0, 0.050, 0.50, 5.0, and 50 ng, respectively). Analyzed mRNAs were as follows; spot 6, mRNA before HPLC purification prepared with no cap analog; 7, Cap(−); 8, TriPure_0; 9, TriPure_1; 10, TetraPure_2; 11, TetraPure_2/m6A; 12, Tri_1; 13, Tri_1/AnP; 14, Tetra_2; 15, Tetra_2/AnP. a‒i Each experiment was repeated independently at least three times to obtain similar results. Source Data were provided with this paper.