The present invention relates to an expression cassette encoding a fusion protein comprising a nucleotide sequence encoding an amino acid sequence shown in SEQ ID NO: 1 or a fragment thereof, which directs protein decay, or encoding an amino acid sequence which is at least 60% identical to the amino acid sequence which directs protein decay; and also comprising a nucleotide sequence encoding a protein of interest, wherein the nucleotide sequences are fused together in frame. Further, the present invention relates to a vector comprising the expression cassette, a host cell comprising the expression cassette or a host cell comprising the vector which comprises the expression cassette. Additionally, the present invention relates to a method for the production of a triterpenoid using the host cell comprising the expression cassette of the present invention.