Regulation of Gene Expression 1. Operon Circuits in Bacteria and other Prokaryotes

Different genes in an organism are meant for the synthesis of different proteins. All these proteins are not needed at one time. Specific enzymes are needed at different times in the life cycle of an organism. However, at all times in the life cycle, every cell contains same set of genes. It would be necessary, therefore, to have mechanisms which would allow only the desired genes to function at a particular time. The activity of other genes will have to be restricted. A variety of mechanisms are now known, which regulate gene expression at different levels including transcription, processing of mRNA and translation. Although information on regulation was available from bacteria for quite some time, only in recent years, work in this area became .possible in eukaryotes. In view of this, three separate sections (one each to bacteria, bacteriophages and eukaryotes) are devoted to this growing area of the regulation of gene, expression. this section is devoted mainly to bacteria.