Signal transduction has been pivotal in our understanding of normal cellular processes in all kingdoms of life.During the last more than three decades,many of the molecules called as signal proteins that transmit signals across the plasma membrane to the nucleus have been identified and characterized.Through these advances,topics such as the cell cycle,apoptosis,cancer and development have been linked.The recent research focused on the molecular mechanisms behind these signalling pathways and their functions in disease,including the design of mechanism-based treatments.However,it is still a big challenge for us to obtain more amount and more pure signal proteins directly from biological organisms.Most of signal proteins used as experimental tools in the laboratories at present are fused ones,which can be purified through cloning,PCR,expressing and isolation.But the procedures are taugh,tedious and time-consuming.