[1] NCI, Macromol Crystallog Lab, Frederick, MD 21702 USA
[2] NIH, Ctr Informat Technol, Sci Comp Branch, Bethesda, MD 20892 USA
[3] NCI, Lab Mol Immunoregulat, Canc Res Ctr, Basic Res Program,SAIC Frederick Inc, Ft Detrick, MD 21702 USA
[4] Univ Maryland, Inst Human Virol, Inst Biotechnol, Baltimore, MD 21201 USA