Sat 28 Feb 2009
What is the spatial relationship between a repressor binding site and a promoter?
Posted by echan76 under Biology
joty asked:
What is the spatial relationship between a repressor binding site and a promoter? How is this different from the spatial relationship between an activator binding site (or enhancer) and a promoter? What properties of DNA allow this difference?
What is the spatial relationship between a repressor binding site and a promoter? How is this different from the spatial relationship between an activator binding site (or enhancer) and a promoter? What properties of DNA allow this difference?
A repressor is a protein which binds to the operator region (reperssor binging region) of DNA in order to prevent transcription. RNA Polymerase travels along the DNA strand and encounters a repressor which gets in the way of transcription. Repressors can “fall off” or attach itself to the operator depending on conditions present in the cell. For example the lac repressor falls off the DNA strand when lactose is present, allowing RNA polymerase to transcribe mRNA which codes of proteins for lactose digestion.
A promoter is a region on the DNA strand which in combination with response elements like hormones has a high affinity to RNA polymerase. It promotes the attachment of RNA polymerase which facilitates the transcription of DNA into mRNA and thus translation into proteins.
Both repressor and promoter act upstream from the protein coding region of a gene. The promoter site being more upstream than the repressor binding site.
The activator binding site can be found anywhere on a chromosome. It does not need to be close to the genes being transcribed to function. It acts by binding activator proteins which help with the binding of RNA polymerase to facilitate transcription. The fact that DNA is structured into chromatin, which is similar to the supercoiled nature of prokaryotic DNA, can make far regions of DNA close to each other and affect each other. In other words the enhancer, even though far away in terms of base pair numbers, can still be close to the promoter in spacial terms.