"If the three carboxy-terminal amino acids of the wild-type luciferase are replaced by a three-amino-acid peroxisome-targeting-avoiding sequence in the mutant, and if the sequence in the mutant is X1X2X3, where X3 is carboxy-terminal, than X1 is any of the twenty amino acids except A, C, G, H, N, P, Q, T and S, X2 is any of the twenty amino acids except H, M, N, Q, R, S and K, and X3 is any of the" . . . .