Formation of the second phosphodiester bond creates a 3-nt product. This transcript is still loosely associated with the RNA polymerase II initiation complex and can dissociate to yield abortive products, which are not further extended. At this stage pausing by RNA polymerase II may result in repeated slippage and reextension of the nascent RNA. The transcription complex still requires continued ATP-hydrolysis by TFIIH for efficient promoter escape. Basal transcription factor TFIIE dissociates from the initiation complex before position +10.
Basal transcription factor TFIIF may reassociate and can stimulate transcription elongation at multiple stages. The open region (“transcription bubble”) expands concomitant with the site of RNA-extension, eventually reaching an open region from -9 to +9.