A G-CSF precursor comprising a signal peptide and a G-CSF peptide, wherein the signal peptide has the sequence of the human wild-type signal peptide of the human G-CSF/b molecule with at least one of the following mutations:deletion of Glu29,insertion of Glu26,substitution Lys11Leu,substitution His21Phe, andsubstitution Gln28Leu.