Addition of the third nucleotide on the nascent transcript

Formation of the second phosphodiester bond creates a 3-nt product. This short transcript is still loosely associated with the RNA polymerase II initiation complex and can dissociate to yield abortive products, which are not further extended. The transcription complex still requires continued ATP-hydrolysis by TFIIH and remains sensitive to single-stranded oligo-nucleotide inhibition.<p>The open region (“transcription bubble”) expands concomitant with the site of RNA-extension. In this case this region spans positions -9 to +3.

第二磷酸二酯键的形成产生了一个由3个核苷酸组成的产物。这一简短转录本仍与RNA聚合酶II的启动复合物松散关联，并可能解离，从而产生非延伸的产物。转录复合物仍需TFIIH持续进行ATP水解，并对单链寡核苷酸抑制保持敏感。在此过程中，开放区域（转录泡）随RNA延伸位点同步扩展。在本例中，该区域横跨-9至+3的位置。