Prokaryotes live in a diversified environment ranging from the human intestine to polluted ponds, rivers, etc. and are thus exposed to different metabolites and molecules. Prokaryotes can survive in such a wide range of ecological conditions because of their ability to ‘switch on’ and ‘switch off’ the expression of specific sets of genes in response to the specific demand of the environment. Prokaryotes regulate the expression of the genes based on their cellular requirements.
Multicellular eukaryotes exhibit differential regulation of gene expression. For example, the B-cells of the immune system produce antibodies, while the pancreatic cells produce insulin. Thus, eukaryotes express a subset of genes in one cell and a different subset in another cell type. Several molecular mechanisms activate the specific portions of the genome and repress the expression of other genes. The inappropriate expression of wrong genes in the wrong place, at the wrong time, in the wrong cell type may lead to deleterious consequences and even death. Thus, regulating the gene expression is of prime importance for the cell and consequently for the organism.