EPSPS or 5-enolpyruvyl-shikimate synthase is an enzyme that catalyzes a reaction in plant and bacterial cells that is necessary for the synthesis of some amino acids. The herbicide, Roundup, can bind to the EPSPS enzyme made in plants and block its ability to work. This causes the plant to run out of amino acids which halts growth and development. The plant eventually dies from starvation. Roundup is a non-selective systemic herbicide which means it injures and often kills most plants that come into contact with it.

The version of EPSPS made in a special strain of Agrobacteria has a slightly altered shape. This alteration prevents Roundup from binding, thus allowing the resistant EPSPS to catalyze the amino acid synthesis reaction. The coding region from the bacterial EPSPS gene was cloned and transferred to plants. Plants with the bacterial EPSPS can thus be sprayed with Roundup and take it up into their cells. Now, they have a backup enzyme that gives them the ability to keep making amino acids and thus resistance to Roundup.
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