In a previous post, we explored some of the properties of promoter sequences and some of the protein domains of RNP holoenzyme. The end product of a search of a DNA sequence for a promoter is the formation of a closed complex. This complex is the first on the path to productive transcription initiation. There are several intermediates in this whole process, and one or more of these reactions is regulated in almost all promoters, though the mechanistic details may differ. To apply knowledge of these steps in understanding regulation of any promoter in particular, we must examine the reaction kinetics of the formation of each of these intermediates. It is also valuable to play around with the parameters to get a feel for the overall process.
The discrete steps were defined and explored through experiment by Will McClure (PNAS, 77, 5634-5638, 1980). Here I will summarise his theoretical approach and a few of his experimental results.