Evidence for RNA template-directed elongation

In vitro cryptic transcription product is often observed when using T7 RNA polymerase. We obtained a ca. 35 mer of cryptic RNA by-product, which was originally designed to be 23 mer by in vitro run-off transcription. Biochemical research and structural analysis indicated that the cryptic by-product was synthesized through the process of aberrant extension by the T7 RNA polymerase. This extension could have occurred through two pathways. One pathway could have been an aberrant termination of transcription, which met a conventional prolonged extension without precise transcription termination, and the other could have been a re-extension of nascent RNA by binding with T7 RNA polymerase.