- Human immunodeficiency virus 1 protease expressed in Escherichia coli behaves as a dimeric aspartic protease. Meek, T.D., Dayton, B.D., Metcalf, B.W., Dreyer, G.B., Strickler, J.E., Gorniak, J.G., Rosenberg, M., Moore, M.L., Magaard, V.W., Debouck, C. Proc. Natl. Acad. Sci. U.S.A. (1989)