Introduction

When the first draft of the human genome sequence became available in February 2001 there was some surprise that instead of 100,000 genes, only about 30,000 genes were counted.  Whole genome sequencing has contributed to the demise of the paradigm that a single gene or at most a few of them encode each character or attribute.  On the other hand, there’s ever more evidence that gene regulation is one of the major sources of diversity in the phenotypes seen in nature. Although all cells of one organism contain more or less the same genetic information, some genes are turned on and others are turned off at different locations and times during the life cycle of an organism.

Cis- and trans-acting factors regulate gene expression

The intricate pattern of gene regulation involves molecular signals that act on DNA sequences encoding protein products. Cis-acting molecules act upon and modulate the expression of physically adjacent, operably linked polypeptide-encoding sequences. Trans-acting factors affect the expression of genes that may be physically located very far away, even on different chromosomes. The expression of a particular gene may be regulated by the concerted action of both cis and trans-acting elements.

What is the role of promoters in the regulation network?

The promoters discussed throughout the paper are DNA sequences that bind to the RNA polymerase II enzyme, which is responsible for the generation of RNA.  The promoter region is usually assumed to be the key cis-acting regulatory region that controls the transcription of adjacent coding region(s) into messenger ribonucleic acid (mRNA), which is then directly translated into proteins.   DNA sequences within promoters can be identified as binding sites for trans-acting factors, “transcription factors”, which may cause activation or repression of transcription.