ABORTIVE CYCLING AND THE RELEASE OF POLYMERASE FOR ELONGATION AT THE SIGMA-54-DEPENDENT GLNAP2 PROMOTER

Transcription initiation at the sigma 54-dependent glnAp2 promoter was studied to follow the state of polymerase as RNA synthesis begins. si gma 54 polymerase begins transcription in abortive cycling mode, i.e. after the first bond is made, approximately 75% of the time the short RNA is aborted and synthesis must be restarted. Polymerase is capable of abortive initiation until it reaches a position beyond +3 and befor e +7, at which stage polymerase is released from its promoter contacts and an elongation complex is formed. Initial elongation is accompanie d by two transcription bubbles, one moving with the polymerase and the other remaining at the transcription start site, The sigma 54-associa ted polymerase shows an earlier and more efficient transition out of a bortive initiation mode than prior studies of sigma 70-associated poly merase.