<p style="text-align: justify;">Insect-resistant tomato line 5345 was developed using recombinant DNA techniques to express the insecticidal protein, Cry1Ac, encoded by the <i>cry1Ac</i> gene from the soil bacterium <i>Bacillus thuringiensis</i> subsp. kurstaki (B.t.k) 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 lepidopteran species. Following binding, cation-specific pores are formed that disrupt midgut ion flow thereby causing gut paralysis and eventual death from bacterial sepsis. Delta-endotoxins, such as the Cry1Ac protein expressed in tomato line 5345, exhibit highly selective insecticidal activity against a narrow range of lepidopteran pests. 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 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 this transgenic tomato. 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).</p>
