Specificity of RNA chain initiation by bacteriophage T7-induced RNA polymerase

Analysis of the nucleotide sequence at the 5′-triphosphate termini of RNA chains synthesized by T7 RNA polymerase from T7 DNA template indicates that nearly all RNA chains synthesized in this polymerase reaction contain the sequence, pppGpGp. In addition, studies carried out on T7 DNA-dependent ³²PP_i exchange into ribonucleoside triphosphates suggest that immediately following the guanine residues at the 5′-end of RNA formed in the T7 RNA polymerase reaction, there is one or more adenine residues. These results indicate a high degree of specificity of initiation of RNA synthesis by T7 RNA polymerase.