Narrator: This is Science Today. About three percent of our genome encodes a proteolytic enzyme of some sort. These enzymes, or proteases, break down proteins. At the University of California, San Francisco, Dr. Charles Craik, studies the biological function and the natural inhibitors of proteases involved with infectious disease, cancer and development. In fact, Craik's lab helped identify and characterize the HIV protease, which led to the current, therapeutic AIDS drugs.

Craik: There's about twenty different projects going on in the lab. So they range from some of our previous work on HIV protease and some of the protein engineering experiments to some of the cancer projects.

Narrator: Craik's lab has identified a class of proteases on the surface of epithelial cells such as in prostate, colon and breast cancer.

Craik: We're trying to determine what their role is and to find out whether they're an appropriate target for chemotherapeutic intervention to come up with either diagnostics and prognostics for monitoring breast and prostate cancer or perhaps even identifying a target that new drugs could be developed to inhibit those.

Narrator: For Science Today, I'm Larissa Branin.