- Human immunodeficiency virus type 1 has an additional coding sequence in the central region of the genome. Matsuda, Z., Chou, M.J., Matsuda, M., Huang, J.H., Chen, Y.M., Redfield, R., Mayer, K., Essex, M., Lee, T.H. Proc. Natl. Acad. Sci. U.S.A. (1988)