Fig. 5.

Comparative efficiency of Ap₃A and Gp₃A incorporation by E. coli RNA polymerase. RNA was synthesized in vitro by E. coli RNA polymerase holoenzyme in the presence of a mixture of each dinucleoside triphosphate and ATP. The promoter sequence at positions −3, −2, and −1 of the coding strand was AAN, where N = A, G, C, or T. In each case, the product ratio (capped transcripts/uncapped transcripts) was determined by boronate gel electrophoresis and normalized to the substrate ratio (Np₃A/ATP = 2.00). Each value corresponds to the mean of three technical replicates. Error bars represent 1 SD. P ≤ 0.001 for each Ap₃A vs. Gp₃A comparison involving the same AAPu promoter and for each AAA vs. AAG and AAPu vs. AAPy comparison involving the same Np₃A, where Pu = A or G and Py = C or T.