The creation of mRNA transcripts is carefully controlled within the cell. Each DNA coding sequence (gene) is accompanied by an upstream control region, consisting of non-coding DNA sequences. Some of these sequences signal the binding location for RNA polymerase, the enzyme which catalyzes the creation of mRNA. Other sequences are the binding sites for either repressors or promoters, which are proteins that selectively bind to specific DNA sequences within the control region.
Repressor binding sites typically overlap the RNA polymerase binding site--a protein bound to this site physically interferes with the binding of RNA polymerase. Promoter binding sites are typically located some distance from the RNA polymerase binding site, and the binding of a promoter to such a site makes it easier for RNA polymerase to bind and initiate mRNA production.
In many cases, a single gene-control sequence contains several promoter and repressor regions. In this proposal, we make use of only repressor DNA binding proteins.