Insulin precursors, their preparation, and dna sequences, expression vehicles and primers and a process for producing human insulin and analogues

The invention relates to insulin precursors having the amino acid sequence B(1-29)-X₁-X₂-Y₂-Y₁-A(1-21) wherein B(1-29) are the 29 first amino acid residues of the B chain of human insulin, A(1-21) are the 21 amino acid residues of the A chain of human insulin, X₁ represents a peptide bond or one or more amino acid residues, X₂ represents Glu or Asp, and Y₁ and Y₂ each represent Lys or Arg, the positions A6 and A11, A7 and B7 and A20 and B19, respectively, being connected through sulphur bridges, and, optionally, one or more of the amino acid residues of chains B(1-29) and A(1-21) are substituted by another amino acid residue. The insulin precursors are prepared by culturing a yeast strain transformed with a replicable expression vehicle comprising a DNA sequence encoding the insulin precursor and isolating it from the culture medium. The insulin precursors can be converted into human insulin or insulin analogues by enzymatic treatment.