<p style="text-align: justify;">Cotton lines 531, 757, and 1076 (trademark Bollgard&reg;, Ingard&reg;) were developed through specific genetic modifications to be resistant to major caterpillar pests of cotton. The transgenic cotton lines express a modified gene (<i>cry1Ac</i>) that encodes an insecticidal crystalline Cry1Ac delta-endotoxin protein, derived from the soil bacterium <i>Bacillus thuringiensis</i> subsp. <i>kurstaki</i> strain HD73. Insecticidal activity is caused by the selective binding of Cry1Ac protein to specific sites localized on the brush border midgut epithelium of susceptible insect species. Following binding, cation-specific pores are formed that disrupt midgut ion flow and thereby cause gut paralysis and eventual death due to bacterial sepsis. Delta-endotoxins, such as the Cry1Ac protein expressed in cotton lines 531, 757, and 1076, exhibit highly selective insecticidal activity against a narrow range of lepidopteran insects such as cotton bollworm, tobacco budworm and pink bollworm. The specificity of action is directly attributable to the presence of specific receptors in the target insects. There are no receptors for delta-endotoxins of <i>B. thuringiensis</i> on the surface of non-lepidopteran insect guts or mammalian intestinal cells, therefore, livestock animals and humans are not susceptible to these proteins.</p>

<p style="text-align: justify;">An antibiotic resistance marker gene (<i>neo</i>) encoding the enzyme neomycin phosphotransferase II (NPTII), which inactivates aminoglycoside antibiotics such as kanamycin and neomycin, was also introduced into the genome of these plants. This gene was derived from a bacterial transposon (Tn5 transposable element from <i>Escherichia coli</i>) and was included as a selectable marker to identify transformed plants during tissue culture regeneration and multiplication. The expression of the <i>neo</i> gene in these plants has no agronomic significance and the safety of the NPTII enzyme as a food additive was evaluated by the United States Food and Drug Administration in 1994 (US FDA, 1994).<br />
Another selectable marker gene, <i>aad</i> (3&quot;(9)-O-aminoglycoside adenylyltransferase (AAD)), was also inserted into the host genome. This gene, which was not expressed in the plants, was used during the development process to select for bacterial colonies that had been transformed with recombinant plasmid DNA.</p>

<p style="text-align: justify;">Unless otherwise indicated, the information presented here is based on documentation pertaining to cotton line 531.</p>
