The present invention relates to a method for producing a polypeptide. The method includes labeling a molecular probe precursor represented by an amino acid sequence of the formula (1) using a labeling compound capable of labeling a lysine or lysine derivative:(1) Y1-Leu-Ser-Xaa12-Gln-Met-Glu-Glu-Glu-Ala-Val-Arg- Leu-Phe-Ile-Glu-Trp-Leu-Xaa27-Asn-Gly-Y2 where Y1 represents an amino acid sequence represented by the formula (2) or the amino acid sequence represented by the formula (2) with 1 to 8 amino acids from the N-terminus being deleted, Xaa12 represents a lysine or lysine derivative, Xaa27 represents a basic amino acid having no functional group at its side chain that reacts with the labeling compound or represents methyl lysine or acetylated lysine, and Y2 represents an amino acid sequence represented by the formula (3) or the amino acid sequence represented by the formula (3) with 1 to 9 amino acids from the C-terminus being deleted:(2) His-Gly-Glu-Gly-Thr-Phe-Thr-Ser-Asp (3) Gly-Pro-Ser-Ser-Gly-Ala-Pro-Pro-Pro-Ser
