The similarities of bar and pat gene products make them equally applicable for plant engineers

The bar and pat genes, isolated from different Streptomyces species, both encode a phosphinothricin acetyltransferase (PAT) and are widely applied in plant genetic engineering. The genes were expressed in Escherichia con and the corresponding proteins were purified and used for functional and structural comparison. Both proteins are homodimers regardless of whether they are expressed in microorganisms or in plants. They have comparable molecular weights and show immuno-cross-reactivity to their respective polyclonal antisera. The enzymes have a similar substrate affinity towards L-phosphinothricin and do not acetylate any of the other L-amino acids tested. In model digestion experiments using simulated human gastric fluids, their enzymatic activity is decreased within seconds, accompanied by a rapid and complete breakdown of both proteins. These data demonstrate the structural and functional equivalence of the PAT proteins, which is also reflected in the comparable performance of transgenic plants carrying the bar or pat gene.