Abstract: The invention relates to a system for expressing nonribosomal peptide synthetases (NRPSs), polyketide synthases (PKS) or NRPS/PKS hybrid synth(et)ases. NRPS, PKS or hybrids thereof are large multi-domain proteins or multi-domain complexes, the expression of which for the production of peptides often causes difficulties. The invention correspondingly relates to a system for expressing portions of the enzymes which can be assembled post-translationally via protein-protein interactions, introduced in a targeted manner, to form multi-enzyme complexes. The invention discloses protein fragments of such an assembly, and the nucleic acids coding therefor. The invention also relates to a vector system for the protein fragments of the invention and its use for producing functional NRPS/PKS enzyme complexes.