The invention relates to a transcriptionally active recombinant linear polynucleotide encoding a multimeric protein comprising in the following order, a first promoter sequence, a first encoding polynucleotide sequence, a bidirectional regulatory sequence, a second encoding polynucleotide sequence and a second promoter sequence, wherein the first and second encoding polynucleotide sequences are in convergent transcriptional orientation, each encoding polynucleotide sequence encodes a component of the multimeric protein and the bidirectional regulatory sequence is operably linked to the first and second encoding polynucleotide sequences and the multimeric protein is an antibody or fragment thereof and each encoding polynucleotide sequence encodes one or more antibody domains or fragments thereof.