Line 19-51a was developed by recombinant DNA techniques to introduce a<br>sulfonylurea tolerant form of ALS gene, which encodes an acetolactate synthase<br>(ALS) enzyme.  The ALS enzyme produced in these transgenic cotton lines is a<br>resistant form of the similar enzyme present in all plants, bacteria and<br>fungi, and thereby confers resistance or tolerance to sulfonylurea herbicides. <br>The ALS gene used in the cotton line 19-51a is a chimeric gene construct that<br>combines two different ALS genes that both encode herbicide sensitive versions<br>of ALS (Mazur et al. 1987).  Through site directed mutagenesis the tobacco ALS<br>genes were altered to confer resistance to sulfonylurea herbicide.  This<br>recombinant ALS gene designated S4-HrA codes for the resistant from of the ALS<br>enzyme that differs in two amino acids, and confers tolerance to sulfonylurea<br>herbicide in the transgenic cotton line 19-51a.  The transgenic cotton line<br>that is the subject of the petition were developed by a widely used technique<br>called Agro-infection which essentially involves using a plant pathogenic<br>strain of A. tumefaciens, and its disarmed plasmid vector (Hoekema et al.<br>1983; Ooms et al. 1981; Ooms et al. 1982).  The chimeric S4-HrA gene was<br>cloned into A. tumefaciens LBA4404.  The S4-HrA gene was transformed into<br>cotton plant cells via a "disarmed" Ti-plasmid vector.  The variety of cotton<br>that was used in developing the line 19-51a is the cultivar Coker 312.