1. Molecular Aspects of Drug Design Section and Retroviral Replication Laboratory, National Cancer InstituteFrederick, P.O. Box B, Frederick, Maryland 21702, McDaniel College, Westminster, Maryland 21157, Southern Research InstituteFrederick Research Center, 431 Aviation Way, Frederick, Maryland 21701, and Center for Advanced Biotechnology and Medicine and Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey 08854