Uncoupling of initiation and reinitiation rates during HeLa RNA polymerase II transcription in vitro.

RNA polymerase II transcription is influenced both by how rapidly a gene is induced and by the rate at which continuous reinitiation occurs after induction. We show here that in vitro the rates of these two critical steps need not be the same. For activator GAL-AH-dependent HeLa transcription, the rate of assembling a preinitiation complex is significantly slower than the rate of reinitiation. Although reinitiation is rapid, it still requires ATP hydrolysis. This unexpected uncoupling of the rates of initiation and reinitiation implies that in regulating mammalian promoter activity, one must consider separately the controls on initiation during induction and the controls on the subsequent reinitiation events.