The cp4 epsps gene was isolated from the CP4 strain of the common soil bacterium Agrobacterium tumefaciens. The enzyme encoded by the sequence is a version of EPSPS that is highly tolerant to inhibition by glyphosate and therefore leads to increased tolerance to glyphosate-containing herbicides. The following reaction is catalyzed by EPSPS:

3-phosphoshikimate + phosphoenolpyruvate = 5-O-(1-carboxyvinyl)-3-phosphoshikimate + phosphate

Glyphosate specifically binds to and inactivates the enzyme EPSPS, which is part of an important plant biochemical pathway called the shikimate pathway. The shikimate pathway is involved in the biosynthesis of the aromatic amino acids tyrosine, phenylalanine and tryptophan, as well as other aromatic compounds. When plants are treated with glyphosate herbicides they cannot produce the aromatic amino acids that are essential to their survival and, therefore, die.

LMOs containing the glyphosate-tolerant epsps gene allow farmers to use glyphosate-containing herbicides for weed control, which will kill the weeds but not the LMO.