Polypeptide producing cells

A method for the production of a heterologous polypeptide or protein encoded by a nucleic acid, said method comprising;

• a) providing a eukaryotic cell,
• b) transfecting said eukaryotic cell with a nucleic acid, wherein the nucleic aid comprises in a 5′ to 3′ direction
• i) a first nucleic acid encoding an immunoglobulin heavy chain without an in frame stop codon at its 3′ terminus,
• ii) a second nucleic acid beginning with a 5′ splice donor site and terminated by a 3′ splice acceptor site comprising an in frame translational stop codon and a polyadenylation signal of a human or mouse immunoglobulin α, ε, γ and μ heavy chain, and
• iii) a third nucleic acid encoding at least 60% of a complete human immunoglobulin transmembrane stretch,
• wherein said immunoglobulin heavy chain and a marker are expressed from the same nucleic acid, wherein the marker is a plasma-membrane bound form of the expressed immunoglobulin heavy chain,
• c) culturing said transfected cell under conditions suitable for the expression of said nucleic acid, and
• d) recovering said polypeptide or protein from the culture medium or the cytoplasm of the cells.