As with other B. thuringiensis-derived delta-endotoxins, the Cry1Ac and Cry2Ab proteins exert their insecticidal activity by binding to specific receptors located on the brush border midgut epithelium of susceptible insect species. Following binding, cation-specific pores are formed that disrupt midgut ionic equilibrium leading to gut paralysis and eventual death due to bacterial sepsis. Cry1Ac and Cry2Ab are highly selective and are only active against Lepidopteran insects. These proteins do, however, interact with different receptor sites in the target insects and it is expected that “stacking” these traits will result in increased protection against insect attack and a delay in the development of resistant insect populations.

In addition to the cry genes conferring insect resistance, MON15985 also contains the nptII and aad selectable marker genes (derived from the parental cotton line containing event MON531) and the beta-D-glucuronidase (GUS) encoding uidA gene from E. coli. This latter gene was introduced as a visually scorable marker gene to identify transformed plantlets in tissue culture. The GUS enzyme can be used to catalyze a colorimetric reaction resulting in the production of a blue colour in transformed cells.