Gene Expression Control by Chromatin Binding Factors

In nature, the hereditary material that contains the instructions for making all living matter is known as deoxyribonucleic acid (DNA). Almost all the cells in our body, except mature red blood cells, have DNA of which the vast majority is located in the nucleus. DNA is composed of long stretches of nucleotides, which themselves are build up of sugar (deoxyribose), phosphate, and two kinds of nucleobases, i.e. purines and pyrimidines. The purine bases comprise adenine (A) and guanine (G), whereas the pyrimidines consist of cytosine (C) and thymine (T). In general, DNA is formed by two nucleotide strands which together assemble into a double helix structure (Watson and Crick, 1953). Within this double-stranded helix, the nucleobases present in opposite strands form hydrogen bonds with each other in such a way that adenine forms base pairs with thymine (A-T) and cytosine pairs up with guanine (C-G). As a consequence of this base pairing, the nucleobases adenine and thymine and cytosine and guanine are present in approximately equal amounts, with A and T each accounting for roughly 30%, whereas C and G each make up 20% of the four bases in human (Chargaff et al., 1950). The relative amounts of A, G, C, and T and, therefore, the composition of DNA vary from one species to another though. The DNA can be divided into several functional domains, such as genic and non-genic regions. The genic regions contain genes, which are pieces of DNA encoding either protein or non-coding ribonucleic acid (ncRNA). In case of the protein-coding genes, information embedded within these genes is transmitted by an intermediate molecule, the messenger RNA (mRNA). This occurs through a process called transcription, which will be explained in more detail later on. The non-genic regions often fulfill regulatory functions which are important for gene transcription.