Construction and Expression of Multiple-copy Expression Cassette of Human Bone Morphogenetic Protein 4

To understand the effect of gene dosage of human bone morphogenetic protein 4(hBMP4) on expression levels in Pichia pastoris,recombinant plasmids carrying 1,3,6,9 expression cassette copies of hBMP4 mature peptide DNA sequence were constructed with unique Bgl Ⅱ and BamH Ⅰ sites shared 4 bases in common between their recognition sites in pAO815 vector in vitro.Then these recombinant plasmids were transformed into Pichia pastoris to analyze expression levels of hBMP4 in Pichia pastoris.The results showed that the highest expression levels of recombinant hBMP4 were achieved by a 1-copy strain,expression levels of hBMP4 were found to decrease for high copy strains in Pichia pastotis.