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, b oth encode a phosphinothricin acetyltransferase (PAT) and are widely a pplied in plant genetic engineering. The genes were expressed in Esche richia con and the corresponding proteins were purified and used for f unctional and structural comparison. Both proteins are homodimers rega rdless of whether they are expressed in microorganisms or in plants. T hey have comparable molecular weights and show immuno-cross-reactivity to their respective polyclonal antisera. The enzymes have a similar s ubstrate affinity towards L-phosphinothricin and do not acetylate any of the other L-amino acids tested. In model digestion experiments usin g simulated human gastric fluids, their enzymatic activity is decrease d within seconds, accompanied by a rapid and complete breakdown of bot h proteins. These data demonstrate the structural and functional equiv alence of the PAT proteins, which is also reflected in the comparable performance of transgenic plants carrying the bar or pat gene.