mCry3A delta-endotoxin is a synthetic, maize optimized, modified cry3A (mcry3A) gene whose expression produces a mCry3A insect control protein that is a member of a class of proteins which occur naturally in the gram-positive soil bacterium Bacillus thuringiensis subsp. tenebrionis.

Additional changes in this maize-optimized gene were made, such that the mCry3A protein has enhanced activity against the western corn rootworm and other related pests: (1) its N-terminus corresponds to methionine-48 of the native protein and (2) a cathepsin-G protease recognition site has been introduced, beginning at amino acid residue 155 of the native protein. This cathepsin-G recognition site has the sequence alanine-alanine-proline-phenylalanine, and has replaced the amino acids valine-155, serine-156, and serine-157 in the native protein. The consensus recognition site for cathepsin-G was determined to be alanine-alanine-proline-phenylalanine.