Prodn. of polypeptides of formula (Gly)q-(X1---X3) (I) is effected by clearing a fusion protein of formula (Y1---Ym)-(Gly) p+q-(X1---Xn) (II) with a polyglycine-specific endoprotease (III): (In the formulae X and Y are natural amino acids; m and n are integers greater than 1; p and q are integers greater than O such that p+q = 2-100, or p may be O and p+q may be less than 2 when Ym= Gly, or q may be O and p+q may be less than 2 when X1=Gly.) 
VERFAHREN ZUR SELEKTIVEN SPALTUNG VON FUSIONSPROTEINEN.