Abstract: DNA molecule and process for producing insulin precursors having the formula B(1-29) -H.sub.1 --X.sub.2 --Y.sub.2 --Y.sub.1 --A(1-21), wherein B(1-29) are the 29 first amino acid residues of the B chain of human insulin starting from the N-terminus, A(1-21) are the 21 amino acid residues of the A chain of human insulin, X.sub.1 represents a peptide bond or one naturally-occurring alpha-amino acid acid residues, X.sub.2 represents Glu or Asp, and Y.sub.1 and Y.sub.2 each represent Lys or Arg, the positions A6 and A11, A7 and B7 and A20 and B19, respectively, are connected through sulphur bridges, and, if desired, one or more of the glutamic acid residues in positions A4, A17, B13 and B21 are substituted by another naturally-occurring alpha-amino acid residue having an uncharged side chain, are provided.

Abstract: Insulin precursors characterized by the amino acid sequence B(1-29)-X.sub.1 -X.sub.2 -Y.sub.2 -Y.sub.1 -A(1-21), wherein B(1-29) are the 29 first amino acid residues of the B chain of human insulin starting from the N-terminus, A(1-21) are the 21 amino acid residues of the A chain of human insulin, X.sub.1 represents a peptide bond or one or more arbitrary amino acid residues, X.sub.2 represents Glu or Asp, and Y.sub.1 and Y.sub.2 each represents Lys or Arg, the positions A6 and A11, A7 and B7 and A20 and B19, respectively, are connected through sulphur bridges, and, if desired, one or more of the amino acid residues of the chains B(1-29) and A(1-21) are substituted by another amino acid residue, are provided. The insulin precursors are prepared by culturing a yeast strain transformed with a replicable expression vehicle comprising a DNA sequence encoding an insulin precursor of the above formula in a suitable medium and isolating the insulin precursor thus formed from the culture medium.