General Transcription Factors Vs. Gene Specific Factors

In eukaryotic cells, a general set of transcription factors is needed to bind RNA polymerase onto the correct region of the DNA to start transcription. These proteins are known as general transcription factors, which form an a complex with the polymerase at the promoter site.

This initial binding must occur at all genes, and occurs at the TATA box, located near the start point of transcription. This binding, however, is not sufficient to start transcription of the gene. Gene expression is highly regulated, especially during development. So, additional binding of gene specific regulatory proteins are needed elsewhere in the cis regulatory regions.

For any gene, its activation is due to a combiniation of SPECIFIC gene regulatory proteins binding to individual sites in the control regions. These regulatory sites can be within the promotor region, adjacent to the TATA box, or at sites outside of the immediate promotor region, and may in fact be thousands of base pairs away from the start point of transcription. This is possible because it is thought that DNA can form loops, bringng the sites closer to the proximity of the promoter region, and hence RNA polymerase. This is yet another way that the regulation of gene expression can occur.