A fragment of a wild-type polypeptide is sequenced for seven amino acids. The same polypeptide region is sequenced in four mutants. Wild-type polypeptide N . . . Thr–His–Ser–Gly–Leu–Lys–Ala . . . C Mutant 1 N . . . Thr–His–Ser–Val–Leu–Lys–Ala . . . C Mutant 2 N . . . Thr–His–Ser–C Mutant 3 N . . . Thr–Thr–Leu–Asp–C Mutant 4 N . . . Thr–Gln–Leu–Trp–Ile–Glu–Gly . . . Determine the wild-type mRNA sequence.