Regulation of Gene Expression Think of it as an on/off switch. The ability of bacteria to regulate their genes depending on the environment has been of great interest to the scientific community and may help us better understand how to combat infection. Many bacteria have the ability to synthesize enzymes needed to make certain products that allow for resistance to antibiotics. But how is this controlled? How do bacteria know when to turn these features on or off? The answer often lies within regulation of gene express. In bacteria, gene expression is controlled at the DNA level. More specifically, proteins control the transcription of messenger RNA which contain the genes for various factors that allow for cell survival. These genes that are controlled can be divided into two categories; Inducible and Repressible. Inducible genes are those that are expressed in the presence of a substance known as an inducer. A well known example of inducible genes is the lactose operon or "lac" operon. This operon contains genes that code for enzymes that are responsible for breaking down lactose. courtesy of http://bioweb.uwlax.edu/genweb/molecular/theory/transcription/transcription.htm Repressible genes are those that shut off expression in presence of a substance known as a co-repressor. They are usually involved in the metabolism of that substance. An example of a repressible gene is the tryptophan "trp" operon which controls the expression of trypophan. courtesy of http://en.wikipedia.org/wiki/Trp_operon Bacteria use these mechanisms to enable them to get what they need and pull back when they have enough. These are just two examples of how bacteria might control their genes based on their environment. There are many more examples and many left to be discovered.