Roundup Ready™ maize

The GA21 line of maize was engineered to be tolerant of glyphosate-containing herbicides. The isolated endogenous maize epsps gene was modified through site-directed mutagenesis, such that its encoded enzyme was insensitive to inactivation by glyphosate, and inserted into the inbred AT maize variety. The modified maize line permits farmers to use glyphosate-containing herbicides for weed control in the cultivation of maize.

pDPG434

The rice actin promoter contains the last 148bp of the 3' end of the rice actin promoter including the rice actin intron.  The 5-enolpyruvyl shikimate-3-phosphate synthase (epsps) gene from maize was modified through site-directed mutagenesis, such that its encoded enzyme was insensitive to inactivation by glyphosate.

Southern blot analysis indicated that the transformed DNA integrated into the host genome at a single site. Analysis further indicated that no sequences from the vector backbone were integrated into the host genome.

Analysis regarding the precise elements that were inserted into the recipient organism is not consistent amongst the various documents.

One set of analysis indicated that two complete copies and one partial copy of the transformation cassette were integrated at a single site into the host genome. The partial copy was composed of the rice actin promoter and the EPSPS coding sequence but not the nos terminator element.

Another set of analysis indicated that the following elements were integrated into the recipient organism:
• a mepsps gene cassette, truncated at the 5' end of the rice actin promoter sequence;
• three complete internal mepsps gene cassettes;
• a partial mepsps gene cassette containing the promoter, intron, otp, and a partial mepsps coding sequence terminating in a stop codon; and
• an additional partial gene cassette at the 3' end containing only the rice actin promoter and 5' mRNA leader sequence, but truncating before the start of the rice actin intron, followed by maize genomic DNA.

Glyphosate specifically binds to and inactivates the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (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 conventional plants are treated with glyphosate they cannot produce the aromatic amino acids essential to their survival. The EPSPS enzyme is present in all plants, bacteria and fungi, but not in animals, which do not synthesize their own aromatic amino acids. Thus, EPSPS is normally present in foods derived from plant and microbial sources.