How does a RNAP locate a specific gene? For instance, growth hormone has to be produced and the RNAP has to locate the gene. But the promoter (TATA box) will also be present infront of all cistrons. So how does the RNAP choose the specific gene? Are the promoters specific for specific gene?
It could be difficult for RNApol to access genes inactivated because inactivated genes are often tightly packed by chromatin. Many genes have enhancer elements(specific DNA sequences) as well as TATA, and transcriptional enhancers, which are proteins, would recognize enhancer elements in a sequence dependent manner and loosen chromatin structure to make RNApol access TATA sequences easily. Transcriptional enhancers also bind to the General Transcriptional Factor complex (GTF), which contains RNApol, therefore enhancers could bring RNApol to TATA sequences. Many tissue specific and/or developmentally-regulated transcriptional enhancers are identified. You could say transcriptional enhancers regulate RNApol which to bind.