Recombinant proteins are proteins that are obtained by the application of recombinant DNA or recombinant RNA. The access pathway includes in vitro and in vivo. The premise of both methods is to apply gene recombination technology to obtain a recombinant vector connecting a gene fragment that can be translated into a target protein, and then transfer it into a host cell that can express the target protein to express a specific recombinant protein molecule. Now protein expression is achieved by a recombinant expression system often E.coli, and has been optimized for protein expression of wild type sequence or a fusion tagged version. In the process of protein expression technology, it has become increasingly common for eukaryotic expression.