DNA Surprise

The Monsanto Co., now a division of Pharmacia Corp., recently admitted that its Roundup Ready soybeans contain two extra bacterial DNA sequences derived from the original transformation event about 10 years ago. The genetically modified (GM) plants are tolerant to Monsanto's herbicide Roundup, or glyphosate, so farmers can kill bothersome weeds without harming their crop. Plants manufacture essential aromatic amino acids such as phenylalanine through the shikimic acid pathway, housed in t

Barry Palevitz
Jul 23, 2000

The Monsanto Co., now a division of Pharmacia Corp., recently admitted that its Roundup Ready soybeans contain two extra bacterial DNA sequences derived from the original transformation event about 10 years ago. The genetically modified (GM) plants are tolerant to Monsanto's herbicide Roundup, or glyphosate, so farmers can kill bothersome weeds without harming their crop.

Plants manufacture essential aromatic amino acids such as phenylalanine through the shikimic acid pathway, housed in their chloroplasts. Glyphosate blocks a key enzyme in the pathway, 5-enolpyruvylshikimate-3-phosphate synthase, or EPSPS. No enzyme activity means no aromatic amino acids--ergo no go.

Monsanto discovered a gene for glyphosate-resistant EPSPS in Agrobacterium species CP4 (U.S. patent #5633435), and through the wonders of genetic engineering, inserted it into soybean's nucleus along with appropriate controlling sequences. A transit peptide lets the cytoplasmically made protein enter chloroplasts. The original transgenic soybean line was called GTS 40-3-2, but the new findings affect...

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