The crystal structure of a ternary complex of human _nununodeficiency virus type 1 reverse transcriptase (HIV-1 RT) heterodimer (p66/p5i), a 19-base/18-base doublestranded DNA template-primer, and a monoclonal antibody Fab fragment has been determined at 3.0 A resolution. (40)(41)(42)(43)(44)(45). The most numerous nucleic acid interactions with protein occur primarily along the sugar-phosphate backbone of the DNA and involve amino acid residues of the palm, thumb, and ringers of p66. Highly conserved regions are located in the p66 palm near the polymerase active site. These structural elements, together with two a-helices of the thumb of p66, act as a clamp to position the template-primer relative to the polymerase active site. The 3'-hydroxyl of the primer terminus is close to the catalytically essential Asp-110, Asp-185, and Asp-186 residues at the active site and is in a position for nudeophilic attack on the a-phosphate of an incoming nucleoside triphosphate. The structure of the HIV-1 RT/DNA/Fab complex should aid our understanding of general mechanisms of nucleic acid polymerization. AIDS therapies may be enhanced by a fuller understanding of drug inhibition and resistance emerging from these studies. A 3.5 A resolution structure of HIV-1 RT complexed with the nonnucleoside inhibitor nevirapine has been reported (8).Although the resolution of the study was not sufficient to determine the position of every amino acid and their side chains, the overall folding of the enzyme was described.We have prepared crystals of a ternary complex (9) of the HIV-1 RT p66/pSl heterodimer, a double-stranded DNA (dsDNA) template-primer, and the antigen-binding fragment (Fab fragment) ofa noninhibiting antibody that diffract x-rays to 2.8 A resolution, and reported the structure ofthis complex at 7 A resolution (10). At this resolution it was possible to determine the location ofthe template-primer and the relative positions of the polymerase and the RNase H active sites. In addition, it was shown that when the nucleic acid substrate was bound to RT a significant portion of the protein moved out of the nucleic acid-binding site.Here we report the structure of the RT-dsDNA-Fab28 complex at 3.0 A resolution. The overall arrangement of the enzyme is similar to that previously reported (8 ITo whom reprint requests should be addressed

We report the first atomic resolution structure of an animal virus, human rhinovirus 14. It is strikingly similar to known icosahedral plant RNA viruses. Four neutralizing immunogenic regions have been identified. These, and corresponding antigenic sequences of polio and foot-and-mouth disease viruses, reside on external protrusions. A large cleft on each icosahedral face is probably the host cell receptor binding site.

WIN 51711 and WIN 52084 are structurally related, antiviral compounds that inhibit the replication of rhino (common cold) viruses and related picornaviruses. They prevent the pH-mediated uncoating of the viral RNA. The compounds consist of a 3-methylisoxazole group that inserts itself into the hydrophobic interior of the VP1 beta-barrel, a connecting seven-membered aliphatic chain, and a 4-oxazolinylphenoxy group (OP) that covers the entrance to an ion channel in the floor of the "canyon." Viral disassembly may be inhibited by preventing the collapse of the VP1 hydrophobic pocket or by blocking the flow of ions into the virus interior.

Nearly 20 percent of the packaged RNA in bean-pod mottle virus (BPMV) binds to the capsid interior in a symmetric fashion and is clearly visible in the electron density map. The RNA displaying icosahedral symmetry is single-stranded with well-defined polarity and stereochemical properties. Interactions with protein are dominated by nonbonding forces with few specific contacts. The tertiary and quaternary structures of the BPMV capsid proteins are similar to those observed in animal picornaviruses, supporting the close relation between plant comoviruses and animal picornaviruses established by previous biological studies.

The structure of Mengo virus, a representative member of the cardio picornaviruses, is substantially different from the structures of rhino- and polioviruses. The structure of Mengo virus was solved with the use of human rhinovirus 14 as an 8 A resolution structural approximation. Phase information was then extended to 3 A resolution by use of the icosahedral symmetry. This procedure gives promise that many other virus structures also can be determined without the use of the isomorphous replacement technique. Although the organization of the major capsid proteins VP1, VP2, and VP3 of Mengo virus is essentially the same as in rhino- and polioviruses, large insertions and deletions, mostly in VP1, radically alter the surface features. In particular, the putative receptor binding "canyon" of human rhinovirus 14 becomes a deep "pit" in Mengo virus because of polypeptide insertions in VP1 that fill part of the canyon. The minor capsid peptide, VP4, is completely internal in Mengo virus, but its association with the other capsid proteins is substantially different from that in rhino- or poliovirus. However, its carboxyl terminus is located at a position similar to that in human rhinovirus 14 and poliovirus, suggesting the same autocatalytic cleavage of VP0 to VP4 and VP2 takes place during assembly in all these picornaviruses.