B i.e. Genes for protease inhibitors Expression vector is a vector which synthesize/produce/express the protein coded by a gene introduced DNA recombination technology. So it is used to produce protein by genetic engineering and detect specific c-DNA molecules in library. Expression vectors are specially constructed so that they contain very active inducible promoters, proper in phase translation initiation codons, both transcription & translation termination signalsQ (to increase transcription & translation) and appropriate protein processing signals, if needed (to produce processed function protein). To enhance the final yield of protein product, some expression vectors even contain genes that code for protease inhibitorsQ.