HIV-1 transcription complex containing 4 nucleotide long transcript HIV-1 transcription complex containing 3 nucleotide long transcript NTP Addition of the fourth nucleotide on the nascent HIV-1 transcript: Second Transition Authored: Matthews, L, Rice, AP, 2005-07-27 00:00:00 EC Number: 2.7.7.6 Edited: Matthews, L, 2005-07-26 23:29:22 Formation of the third phosphodiester bond creates a 4-nt product. This commits the initiation complex to promoter escape. The short 4-nt transcript is still loosely associated with the RNA polymerase II initiation complex and can dissociate to yield abortive products, which are not further extended. Inhibition of ATP-hydrolysis by TFIIH does not lead to collapse of the open region any longer. The transcription complex has lost the sensitivity to single-stranded oligo-nucleotide inhibition. However, ATP-hydrolysis and TFIIH are required for efficient promoter escape. The open region (“transcription bubble”) expands concomitant with the site of RNA-extension. In this case this region spans positions -9 to +4. Reactome Database ID Release 43167113 Reactome, http://www.reactome.org ReactomeREACT_6184