The rational design of drugs that can inhibit the action of viral proteases depends on obtaining accurate structures of these enzymes. The crystal structure of chemically synthesized HIV-1 protease has been determined at 2.8 angstrom resolution (R factor of 0.184) with the use of a model based on the Rous sarcoma virus protease structure. In this enzymatically active protein, the cysteines were replaced by alpha-amino-n-butyric acid, a nongenetically coded amino acid. This structure, in which all 99 amino acids were located, differs in several important details from that reported previously by others. The interface between the identical subunits forming the active protease dimer is composed of four well-ordered beta strands from both the amino and carboxyl termini and residues 86 to 94 have a helical conformation. The observed arrangement of the dimer interface suggests possible designs for dimerization inhibitors.

The structure of a complex between a peptide inhibitor with the sequence N-acetyl-Thr-Ile-Nle-psi[CH2-NH]-Nle-Gln-Arg.amide (Nle, norleucine) with chemically synthesized HIV-1 (human immunodeficiency virus 1) protease was determined at 2.3 A resolution (R factor of 0.176). Despite the symmetric nature of the unliganded enzyme, the asymmetric inhibitor lies in a single orientation and makes extensive interactions at the interface between the two subunits of the homodimeric protein. Compared with the unliganded enzyme, the protein molecule underwent substantial changes, particularly in an extended region corresponding to the "flaps" (residues 35 to 57 in each chain), where backbone movements as large as 7 A are observed.

Activator protein-1 (AP-1) is a transcription factor that consists of either a Jun-Jun homodimer or a Jun-Fos heterodimer. Transactivation of AP-1 is required for tumor promoter-induced transformation in mouse epidermal JB6 cells and for progression in mouse and human keratinocytes. Until now, the question of whether AP-1 transactivation is required for carcinogenesis in vivo has remained unanswered, as has the issue of functionally significant target genes. To address these issues we have generated a transgenic mouse in which transactivation mutant c-jun (TAM67), under the control of the human keratin-14 promoter, is expressed specifically in the basal cells of the epidermis where tumor induction is initiated. The keratin-14-TAM67 transgene was expressed in the epidermis, tongue, and cervix, with no apparent abnormalities in any tissue or organ. TAM67 expression blocked 12-O-tetradecanoylphorbol 13-acetate (TPA, phorbol 12-tetradecanoate 13-acetate) induction of the AP-1-regulated luciferase in AP-1 luciferase͞TAM67 mice, but did not inhibit induction of candidate AP-1 target genes, collagenase-1 or stromelysin-3. More interestingly, TAM67 expression did not inhibit TPA-induced hyperproliferation. In twostage skin carcinogenesis experiments, the transgenic animals showed a dramatic inhibition of papilloma induction. We conclude that transactivation of a subset of AP-1-dependent genes is required for tumor promotion and may be targeted for cancer prevention.