The specificities of the proteases of 11 retroviruses were studied using a series of oligopeptides with amino acid substitutions in the P1, P3, and P4 positions of a naturally occurring type 1 cleavage site (Val-Ser-GlnAsn-Tyr2Pro-Ile-Val-Gln) in human immunodeficiency virus type 1 (HIV-1). Previously, the substrate specificity of the P2 site was studied for the same representative set of retroviral proteases, which included at least one member from each of the seven genera of the family Retroviridae (P. Bagossi, T. Sperka, A. Fehér, J. Kádas, G. Zahuczky, G. Miklóssy, P. Boross, and J. Tözsér, J. Virol. 79:4213-4218, 2005). Our enzyme set comprised the proteases of HIV-1, HIV-2, equine infectious anemia virus, avian myeloblastosis virus (AMV), Mason-Pfizer monkey virus, mouse mammary tumor virus (MMTV), Moloney murine leukemia virus, human T-lymphotropic virus type 1, bovine leukemia virus, walleye dermal sarcoma virus, and human foamy virus. Molecular models were used to interpret the similarities and differences in specificity between these retroviral proteases. The results showed that the retroviral proteases had similar preferences (Phe and Tyr) for the P1 position in this sequence context, but differences were found for the P3 and P4 positions. Importantly, the sizes of the P3 and P4 residues appear to be a major contributor for specificity. The substrate specificities correlated well with the phylogenetic tree of the retroviruses. Furthermore, while the specificities of some enzymes belonging to different genera appeared to be very similar (e.g., those of AMV and MMTV), the specificities of the primate lentiviral proteases substantially differed from that observed for a nonprimate lentiviral protease.

Most tumor cells attain their immortality by reactivating telomerase. We report here the telomerase inhibitory potential of chimeric oligonucleotides composed of a 13mer antisense sequence targeting the telomerase RNA template region and a (s 4 dU) n moiety at its 3 0 or 5 0 -end. The increase of the thiolated chain length enhances the telomerase inhibitory potential, but decreases specificity, indicated by HIV reverse transcriptase inhibition. Chimeras with 5 0 (s 4 dU) n s were more potent inhibitors than the antisense alone or the 3 0 modified ones. Cy5-labeled (s 4 dU) 4 AS and (s 4 dU) 8 AS proved the internalization of the oligonucleotides, raising the possibility to be tested as cellular anti-telomerase agents.

To explore the role of residues being close to the catalytic aspartates in the higher pH optimum and in the lower dimer stability of human foamy virus (HFV) protease (PR) in comparison with human immunodeficiency virus type 1 (HIV-1) protease, single (Q8R, H22L, S25T, T28D) and double (Q8R-T28D, H22L-T28D) mutants were created based on sequence alignments and on the molecular model of HFV PR. The wild-type and mutant enzymes were expressed in fusion with maltose binding protein in Escherichia coli and the fusion proteins were purified by affinity chromatography. Specificity constant of most mutants was lower, but the value of Q8R-T28D double mutant enzyme was higher than that of the wild-type HFV PR. Furthermore, urea denaturation at two pH values and pH optimum values showed an increased stability and pH optimum for most mutants. These results suggest that the mutated residues may not be responsible for the higher pH optimum of HFV PR, but they may contribute to the lower dimer stability as compared with that of HIV-1 PR.