The Npro Autoprotease technology that has been co-developed by Boehringer Ingelheim and Sandoz is an excellent expression and purification method for improving yields of finicky and hard-to-express proteins, hormones and peptides efficiently from E. coli. The Npro autoprotease enzyme can genetically be fused to the N-terminus of target proteins. The autoprotease enzyme together with the protein of interest is forced into cytoplasmically insoluble inclusion bodies. After recovery and preparation of the inclusion bodies the autoprotease is reactivated during the in vitro refolding procedure. The fusion partner is released from the C-terminal end of the autoprotease by self-cleavage, a process that generates the authentic N-terminus of the target protein.