Interactions in vivo between the Vif protein of HIV-1 and the precursor (Pr55GAG) of the virion nucleocapsid proteins

The abnormality of viral core structure seen in vif-defective HIV-1 grown in PBMCs has suggested a role for Vif in viral morphogenesis. Using an in vivo mammalian two-hybrid assay, the interaction between Vif and the precursor (Pr55GAG) of the virion nucleocapsid proteins has been analysed. This revealed the amino-terminal (aa 1–22) and central (aa 70–100) regions of Vif to be essential for its interaction with Pr55GAG, but deletion of the carboxy-terminal (aa 158–192) region of the protein had only a minor effect on its interaction. Initial deletion studies carried out on Pr55GAG showed that a 35-amino-acid region of the protein bridging the MA(p17)–CA(p24) junction was essential for its ability to interact with Vif. Site-directed mutagenesis of a conserved tryptophan (Trp21) near the amino terminus of Vif showed it to be important for the interaction with Pr55GAG. By contrast, mutagenesis of the highly conserved YLAL residues forming part of the BC-box motif, shown to be important in Vif promoting degradation of APOBEC3G/3F, had little or no effect on the Vif–Pr55GAG interaction

Polymorphisms in Gag spacer peptide 1 confer varying levels of resistance to the HIV- 1maturation inhibitor bevirimat

Background: The maturation inhibitor bevirimat (BVM) potently inhibits human immunodeficiency virus type 1 (HIV-1) replication by blocking capsid-spacer peptide 1 (CA-SP1) cleavage. Recent clinical trials demonstrated that a significant proportion of HIV-1-infected patients do not respond to BVM. A patient’s failure to respond correlated with baseline polymorphisms at SP1 residues 6-8. Results: In this study, we demonstrate that varying levels of BVM resistance are associated with point mutations at these residues. BVM susceptibility was maintained by SP1-Q6A, -Q6H and -T8A mutations. However, an SP1-V7A mutation conferred high-level BVM resistance and SP1-V7M and T8Δ mutations conferred intermediate levels of BVM resistance. Conclusions: Future exploitation of the CA-SP1 cleavage site as an antiretroviral drug target will need to overcome the baseline variability in the SP1 region of Gag.Publisher PDFPeer reviewe

Cleavage of p15 protein in vitro by human immunodeficiency virus type 1 protease is RNA dependent

The human immunodeficiency virus (HIV) gag polyprotein is processed by the viral protease to yield the structural proteins of the virus. One of these structural proteins, p15, and its protease cleavage products, p7 and p6, are believed to be responsible for the viral RNA binding which is prerequisite for assembly of infectious virions. To better understand potential interactions between viral RNA, p15, and the HIV protease, we have synthesized p15 in an in vitro system and studied its processing by the viral protease. Using this system, we demonstrate that p15 synthesized in vitro is properly cleaved by the HIV protease in an RNA-dependent reaction. Mutation of cysteine residues in either zinc-binding domain of the p7 portion of p15 does not alter the RNA-dependent cleavage, but mutation of three basic residues located between the zinc-binding domains blocks HIV protease susceptibility. The results support a previously unrecognized role for the interaction of RNA and nucleocapsid-containing gag precursors that may have important consequences for virus assembly.</jats:p

Thymosin beta arg10, a major variant of thymosin beta 10 in rabbit tissues.

Two homologous peptides, designated thymosin beta 4 and thymosin beta 10, respectively, have been shown to be widely distributed in mammalian cells and tissues (S. Erickson-Viitanen, S. Ruggieri, P. Natalini, and B.L. Horecker (1983) Arch. Biochem. Biophys. 221, 570-576; S. Erickson-Viitanen, S. Ruggieri, P. Natalini, and B.L. Horecker, (1983) Arch. Biochem. Biophys. 225, 407-413). In the rabbit, thymosin beta 4 is replaced by a variant, thymosin beta ala4, that contains alanine in place of serine at the blocked NH2-terminus. It is reported that in rabbit tissues thymosin beta 10 is also replaced by a variant, designated thymosin beta arg10, that contains an additional amino acid, arginine, inserted following lysine-38. The rabbit tissues analyzed also differ from those of other mammals in the relative quantities of thymosin beta ala4 and beta arg10, which are nearly equal, compared to tissues from other mammals where the quantities of thymosin beta 10 are only one-third to one-tenth those of thymosin beta 4