DISCONTINUOUS MECHANISM OF TRANSCRIPTION ELONGATION

During transcription elongation, three flexibly connected parts of RNA polymerase of Escherichia coli advance along the template so that the front-end domain is followed by the catalytic site which in turn is f ollowed by the RNA product binding site. The advancing enzyme was foun d to maintain the same conformation throughout extended segments of th e transcribed region. However, when the polymerase traveled across cer tain DNA sites that seemed to briefly anchor the front-end domain, cyc lic shifting of the three parts, accompanied by buildup and relief of internal strain, was observed. Thus, elongation proceeded in alternati ng laps of monotonous and inchworm-like movement with the flexible RNA polymerase configuration being subject to direct sequence control.