And this is found in our blood clotting cascade. So what thrombin does is it cleaves at the carboxyl side of arginine. And we have many, many more examples of such biological enzymes in our body as well as in other organisms. So let's go back to this question. Once we know what the sequence is of these individual segments, how do we order those segments together? So what we have to do is so we take this polypeptide and we first expose it to one type of cleaving agent, and then we take that same polypeptide again and we expose it to another different type of Cleaving agent.