Bacterial RNA Polymerase
Eukaryotic RNA Polymerase
The promoter region contains important sequences that are required for RNA polymerase to bind. These sequences are similar in both prokaryotic and eukaryotic genes, but the locations are different.
Conserved Sequences in Promoters
As DNA unwinds during bacterial transcription, the transcription apparatus occupies different sites in the gene during different steps of transcription.
DNA Footprinting TechniqueThe RNA polymerase-promoter complex is partially digested by DNase I. The DNA is then labeled on one strand. The fragments are then broken using the Maxam-Gilbert sequencing reagents. A control is run which is treated identically except it consists of the same promoter DNA without the transcription complex attached. The fragmented DNA is then separated on a gel. That region of the promoter sequence in the control that is missing in the complexed DNA defines the region in which the DNA is bound.
Steps in Model Eukaryotic TranscriptionThe adenovirus late promoter requires four accessory factors and RNA Polymerase II to be added to the promoter in a defined manner for transcription to begin. This can be monitored by footprinting analysis to measure the size of the complex. The following table shows the order in which the the four transcription factors and RNA Polymerase II come together to form the protein that will actually transcribe the gene.
For bacterial RNA polymerase, only the sigma factor is needed for the enzyme to recognize the promoter. The eukaryotic transcription factors may indeed act as sigma factors to allow the eukaryoitic RNA polymerase to recognize the promoter. Some of the factors may be specific to certain promoters so groups of factors like these would be expected to exist.
Copyright © 1998. Phillip McClean