Method for production of an oligomeric protein in eukaryotic cells comprising the steps a) Co-expression of two fusion proteins in eukaryotic cells comprising - a first fusion protein comprising a protein and an S-Tag (in the following also called protein-S-Tag fusion protein), wherein the protein is an antigen or an antigen binding unit, wherein the S-Tag of the protein-S-Tag fusion protein has a sequence identity of at least 70% to one of the sequences SEQ ID NO. 2 to 8, and - a second fusion protein comprising a S-protein and a tail piece (tp) (in the following also called S-protein-tail piece (tp) fusion protein), wherein the S-protein of the S-protein-tp fusion protein comprises an oligopeptide with a sequence identity of at least 80% to one of the sequences SEQ ID NO. 9 to 15, wherein the tail piece (tp) is an oligopeptide derived from a heavy chain of an IgM or IgA antibody, wherein the tp of the S-protein-tp fusion protein is selected from sequences with a sequence identity of at least 75% to one of the sequences SEQ ID NO. 16 to 22 or 30 to 34, b) Extraction of the two fusion proteins, wherein oligomerisation of the protein of the protein-S-Tag fusion protein takes place after co-expression in eukaryotic cells according to step a) and/or after extraction according to step b). a) Co-expression of two fusion proteins in eukaryotic cells comprising - a first fusion protein comprising a protein and an S-Tag (in the following also called protein-S-Tag fusion protein), wherein the protein is an antigen or an antigen binding unit, wherein the S-Tag of the protein-S-Tag fusion protein has a sequence identity of at least 70% to one of the sequences SEQ ID NO. 2 to 8, and - a second fusion protein comprising a S-protein and a tail piece (tp) (in the following also called S-protein-tail piece (tp) fusion protein), wherein the S-protein of the S-protein-tp fusion protein comprises an oligopeptide with a sequence identity of at least 80% to one of the sequences SEQ ID NO. 9 to 15, wherein the tail piece (tp) is an oligopeptide derived from a heavy chain of an IgM or IgA antibody, wherein the tp of the S-protein-tp fusion protein is selected from sequences with a sequence identity of at least 75% to one of the sequences SEQ ID NO. 16 to 22 or 30 to 34, - a first fusion protein comprising a protein and an S-Tag (in the following also called protein-S-Tag fusion protein), wherein the protein is an antigen or an antigen binding unit, wherein the S-Tag of the protein-S-Tag fusion protein has a sequence identity of at least 70% to one of the sequences SEQ ID NO. 2 to 8, and wherein the protein is an antigen or an antigen binding unit, wherein the S-Tag of the protein-S-Tag fusion protein has a sequence identity of at least 70% to one of the sequences SEQ ID NO. 2 to 8, and - a second fusion protein comprising a S-protein and a tail piece (tp) (in the following also called S-protein-tail piece (tp) fusion protein), wherein the S-protein of the S-protein-tp fusion protein comprises an oligopeptide with a sequence identity of at least 80% to one of the sequences SEQ ID NO. 9 to 15, wherein the tail piece (tp) is an oligopeptide derived from a heavy chain of an IgM or IgA antibody, wherein the tp of the S-protein-tp fusion protein is selected from sequences with a sequence identity of at least 75% to one of the sequences SEQ ID NO. 16 to 22 or 30 to 34, wherein the S-protein of the S-protein-tp fusion protein comprises an oligopeptide with a sequence identity of at least 80% to one of the sequences SEQ ID NO. 9 to 15, wherein the tail piece (tp) is an oligopeptide derived from a heavy chain of an IgM or IgA antibody, wherein the tp of the S-protein-tp fusion protein is selected from sequences with a sequence identity of at least 75% to one of the sequences SEQ ID NO. 16 to 22 or 30 to 34, b) Extraction of the two fusion proteins,