EloC) through a novel SOCS (suppressor of cytokine signaling)-box that bindsEloC. Vif binding to EloC is negatively regulated by serine phosphorylation in the BC-box motif of the SOCSbox. Vif ubiquitination is promoted by Cul5 in vitro and in vivo, and requires an intact SOCS-box. Thus, autoubiquitination of Vif occurs within the assembled VifCul5 complex, analogous to F-box proteins that are autoubiquitinated within their SCF (Skp1-Cullin-F-box) complex. These findings suggest mechanisms that regulate the assembly and activity of Cul5 E3 complexes through phosphorylation or autoubiquitination of the SOCS-box protein, and identify interactions between Vif and host cell proteins that may be therapeutic targets.Supplemental material is available at http://www.genesdev.org.

Sex in mammals is genetically determined and is defined at the cellular level by sex chromosome complement (XY males and XX females). The Y chromosome-linked gene sex-determining region Y (SRY) is believed to be the master initiator of male sex determination in almost all eutherian and metatherian mammals, functioning to upregulate expression of its direct target gene Sry-related HMG box-containing gene 9 (SOX9). Data suggest that SRY evolved from SOX3, although there is no direct functional evidence to support this hypothesis. Indeed, loss-of-function mutations in SOX3 do not affect sex determination in mice or humans. To further investigate Sox3 function in vivo, we generated transgenic mice overexpressing Sox3. Here, we report that in one of these transgenic lines, Sox3 was ectopically expressed in the bipotential gonad and that this led to frequent complete XX male sex reversal. Further analysis indicated that Sox3 induced testis differentiation in this particular line of mice by upregulating expression of Sox9 via a similar mechanism to Sry. Importantly, we also identified genomic rearrangements within the SOX3 regulatory region in three patients with XX male sex reversal. Together, these data suggest that SOX3 and SRY are functionally interchangeable in sex determination and support the notion that SRY evolved from SOX3 via a regulatory mutation that led to its de novo expression in the early gonad.

Biosimilars remain a hot topic in rheumatology, and some physicians are cautious about their application in the real world. With many products coming to market and a wealth of guidelines and recommendations concerning their use, there is a need to understand the changing landscape and the real clinical and health-economic potential offered by these agents. Notably, rheumatologists will be at the forefront of the use of biosimilar monoclonal antibodies/soluble receptors. Biosimilars offer cost savings and health gains for our patients and will play an important role in treating rheumatic diseases. We hope that these lower costs will compensate for inequities in access to therapy based on economic differences across countries. Since approved biosimilars have already demonstrated highly similar efficacy, it will be most important to establish pharmacovigilance databases across countries that are adequate to monitor long-term safety after marketing approval.

Vif is a 23-kDa protein encoded by human immunodeficiency virus, type 1 (HIV-1) which is important for virion infectivity. Here, we describe the phosphorylation of HIV-1 Vif and its role in HIV-1 replication. In vivo studies demonstrated that Vif is highly phosphorylated on serine and threonine residues. To identify phosphorylation sites and characterize the Vif kinase(s), Vif was expressed in Escherichia coli and purified for use as a substrate in in vitro kinase assays. The purified Vif protein was phosphorylated in vitro on serine and threonine residues by a kinase(s) present in both cytosol and membrane fractions. Phosphorylation of Vif was stimulated by phorbol 12-myristate 13-acetate and inhibited by staurosporine and hypericin, a drug with potent anti-HIV activity. The Vif kinase(s) was resistant to inhibitors of protein kinase C, cAMP-dependent kinase, and cGMP-dependent kinase, suggesting that it is distinct from these enzymes. To identify the phosphorylation sites, 32P-labeled Vif was digested by V8 protease and the peptides were resolved by reverse-phase high performance liquid chromatography. Radioactive peptide sequencing identified three phosphorylation sites within the C terminus, Ser144, Thr155, and Thr188. Two-dimensional tryptic phosphopeptide mapping indicated that these sites are also phosphorylated in vivo. Both Ser144 and Thr188 are contained in the recognition motifs (R/KXXS*/T* and R/KXXXS*/T*) used by serine/threonine protein kinases such as cGMP-dependent kinase and PKC. Ser144 is present in the motif SLQXLA, which is the most highly conserved sequence among all lentivirus Vif proteins. Mutation of Ser144 to alanine resulted in loss of Vif activity and >90% inhibition of HIV-1 replication. These studies suggest that phosphorylation of Vif by a serine/threonine protein kinase(s) plays an important role in regulating HIV-1 replication and infectivity.

The HIV-1 RNA genome is a dimer which consists of two identical strands of RNA linked near their 5' ends by a dimer linkage structure (DLS). We have structurally characterized full-length HIV-1 genomic RNA isolated from HIV-1 virions by electron microscopy. As in other retroviruses, the HIV-1 RNA genome contains a central dimer linkage structure and additional loop structures within each monomer subunit. In contrast to the DLS of other retroviruses, the DLS region of HIV-1 contains a loop of 323 +/- 44 nucleotides. The free 5' ends of the two RNA strands were not visualized, suggesting that the 5' end regions are involved in interstrand complementary base pairing. Computer modeling identified a single stable structure that was consistent with the electron microscopy data. In this model, the two RNA strands are linked at their 5' ends by two contact points derived from "kissing-loop" interactions between r-u5 and SL1 stem-loops and their counterparts on the second strand. These interactions may contribute to the formation of stable HIV-1 RNA dimers in vivo.