A polypeptide selected from the group consisting of (1) a polypeptide having the amino acid sequence represented by SEQ ID NO:1 and (2) a polypeptide having an amino acid sequence derived from the amino acid sequence represented by SEQ ID NO:1 by substitution of the amino acid at the 3-position by another amino acid and having an insulin-like growth factor 1 (IGF-1) activity; a DNA encoding the above polypeptide; a vector containing the above DNA; a host cell containing the above vector; and a method of producing a recombinant protein by using the above polypeptide.