Recently proposed models that have gained wide acceptance posit that HIV-1 virion morphogenesis is initiated by targeting the major structural protein (Gag) to late endosomal membranes. Thereafter, late endosome-based secretory pathways are thought to deliver Gag or assembled virions to the plasma membrane (PM) and extracellular milieu. We present several findings that are inconsistent with this model. Specifically, we demonstrate that HIV-1 Gag is delivered to the PM, and virions are efficiently released into the extracellular medium, when late endosome motility is abolished. Furthermore, we show that HIV-1 virions are efficiently released when assembly is rationally targeted to the PM, but not when targeted to late endosomes. Recently synthesized Gag first accumulates and assembles at the PM, but a proportion is subsequently internalized via endocytosis or phagocytosis, thus accounting for observations of endosomal localization. We conclude that HIV-1 assembly is initiated and completed at the PM, and not at endosomal membranes.

The host range of retroviruses is influenced by antiviral proteins such as TRIM5, a restriction factor that recognizes and inactivates incoming retroviral capsids. Remarkably, in Owl monkeys (omk), a cyclophilin A (CypA) cDNA has been transposed into the TRIM5 locus, resulting in the expression of a TRIM5-CypA fusion protein (TRIMCyp) that restricts retroviral infection based on the retroviral capsid-binding specificity of CypA. Here, we report that the seemingly improbable genesis of TRIMCyp has, in fact, occurred twice, and pigtailed macaques (pgt) express an independently generated TRIMCyp protein. The omkTRIMCyp and pgtTRIMCyp proteins restrict infection by several lentiviruses, but their specificities are distinguishable. Surprisingly, pgtTRIMCyp cannot bind to or restrict HIV-1 capsids as a consequence of a point mutation close to the Cyp:capsid-binding interface that was acquired during or after transposition of pgtCypA. However, the same mutation confers on pgtTRIMCyp the ability to restrict FIV in the presence of cyclosporin A, a drug that normally abolishes the interaction between pgtTRIMCyp or omkTRIMCyp and lentiviral capsids. Overall, an intuitively unlikely evolutionary event has, in fact, occurred at least twice in primates and represents a striking example of convergent evolution in divergent species.HIV-1 ͉ LINE ͉ restriction factor

The inability of human immunodeficiency virus type 1(HIV-1) to replicate in rhesus macaque cells is in part due to the failure of HIV-1 Vif to counteract the restriction factor APOBEC3G. However, in this study we demonstrate that several rhesus macaque APOBEC3 (rhAPOBEC3) proteins are capable of inhibiting HIV-1 infectivity. There was considerable variation in the ability of a panel of Vif proteins to induce degradation of rhAPOBEC3 proteins, and mutations within HIV-1 Vif that render it capable of degrading rhAPOBEC3G did not confer activity against other antiviral rhAPOBEC3 proteins. These findings suggest that multiple APOBEC3 proteins can contribute to primate lentivirus species tropism.

Human polynucleotide kinase (hPNK) is required for processing and rejoining DNA strand break termini. The 5-DNA kinase and 3-phosphatase activities of hPNK can be stimulated by the "scaffold" protein XRCC1, but the mechanism remains to be fully elucidated. Using a variety of fluorescence techniques, we examined the interaction of hPNK with XRCC1 and substrates that model DNA single-strand breaks. hPNK binding to substrates with 5-OH termini was only ϳ5-fold tighter than that to identical DNA molecules with 5-phosphate termini, suggesting that hPNK remains bound to the product of its enzymatic activity. The presence of XRCC1 did not influence the binding of hPNK to substrates with 5-OH termini, but sharply reduced the interaction of hPNK with DNA bearing a 5-phosphate terminus. These data, together with kinetic data obtained at limiting enzyme concentration, indicate a dual function for the interaction of XRCC1 with hPNK. First, XRCC1 enhances the capacity of hPNK to discriminate between strand breaks with 5-OH termini and those with 5-phosphate termini; and second, XRCC1 stimulates hPNK activity by displacing hPNK from the phosphorylated DNA product.Scission of the DNA sugar-phosphate backbone is a common form of damage that can be induced not only by a broad range of genotoxic agents, but also as an intermediate product in several DNA repair pathways. The term "strand break" covers an array of diverse chemical structures. Aside from single-and doublestrand breaks, there are many chemically distinct end groups found at strand break termini. Repair of these strand interruptions is usually mediated by DNA polymerases and ligases. All DNA polymerases and ligases characterized to date are highly selective for the type of DNA ends that can be utilized. Both of these classes of enzymes require 3Ј-hydroxyl DNA termini, and the DNA ligases also require 5Ј-phosphate termini. However, the termini generated by several endonucleases, as well as those induced by ionizing radiation, frequently bear 5Ј-hydroxyl and/or 3Ј-phosphate groups (1-5) and must therefore be processed before they can be acted upon by DNA ligases or polymerases.Mammalian polynucleotide kinase (PNK) 3 /phosphatase is a bifunctional enzyme that can phosphorylate 5Ј-OH termini and dephosphorylate 3Ј-phosphate termini of DNA (6, 7). It is a DNA repair enzyme involved in the processing of strand break termini to a form suitable for other proteins to complete the replacement of missing nucleotides and strand rejoining (8 -11). PNK is implicated in the repair of both single-strand breaks (SSBs) and double-strand breaks. PNK stimulates SSB repair in both in vitro reconstitution experiments (5,10,12,13) and in vivo studies (14). Further evidence has indicated that, as a result of its required involvement in the repair of specific types of SSBs, PNK participates in the base excision repair pathway following the formation of strand breaks induced by DNA glycosylases such as NEIL1 and NEIL2 (5) and in the repair of topoisomerase-1 "dead-end" complexes (15,16). PNK i...

Mammalian cells express several factors that inhibit lentiviral infection and that have been under strong selective pressure. One of these factors, TRIM5, targets the capsid protein of incoming retrovirus particles and inhibits subsequent steps of the replication cycle. By substituting human immunodeficiency virus type 1 capsid, we were able to show that a set of divergent primate lentivirus capsids was generally not susceptible to restriction by TRIM5 proteins from higher primates. TRIM5␣ proteins from other primates exhibited distinct restriction specificities for primate lentivirus capsids. Finally, we identified novel primate lentiviral capsids that are targeted by TRIMCyp proteins.Primates have been colonized by retroviruses at various times during their evolution, leading to the selection of species-specific variants of genes encoding restriction factors that defend host cells from infection. Reciprocally, in order to colonize a particular species, retroviruses have evolved resistance to these species-specific barriers by changing their protein sequences to avoid interactions with restriction factors or by expressing small proteins that specifically neutralize them. However, the specialization involved in overcoming restriction factors present in one host species can come at the expense of acquiring susceptibility to those of another. This could, in principle, limit cross-species transmission. For example, endogenous levels of the capsid (CA)-targeting restriction factor TRIM5␣ do not inhibit human immunodeficiency virus type 1 (HIV-1) replication in humans, yet rhesus TRIM5␣ is a major barrier to HIV-1 replication in rhesus macaque cells (10,12,14,20,24,32). To explore whether TRIM5␣ is a general barrier to cross-species primate lentivirus transmission, we determined the abilities of TRIM5 proteins from various primate species to restrict divergent primate lentiviruses.A limiting factor in undertaking studies of diverse primate lentiviruses is that the complete genome sequence and infectious molecular clones are not yet available for a number of these lentiviruses. Furthermore, the generation of virus isolates and infectious molecular clones often involves passage in human cells, which might lead to the selection of mutations that alter sensitivity to human restriction factors such as TRIM5␣. However, TRIM5 proteins target the viral CA pro-* Corresponding author. Mailing address:

Most guidelines on neonatal skin care emphasize issues pertaining to healthy, term infants. Few address the complex task of skin barrier maintenance in preterm, very preterm, and extremely preterm infants. Here, we provide an evidence‐based review of the literature on skin care of preterm neonates. Interestingly, the stratum corneum does not fully develop until late in the third trimester, and as such, the barrier function of preterm skin is significantly compromised. Numerous interventions are available to augment the weak skin barrier of neonates. Plastic wraps reduce the incidence of hypothermia while semipermeable and transparent adhesive dressings improve skin quality and decrease the incidence of electrolyte abnormalities. Tub bathing causes less body temperature variability than sponge bathing and can be performed as infrequently as once every four days without increasing bacterial colonization of the skin. Topical emollients, particularly sunflower seed oil, appear to reduce the incidence of skin infections in premature neonates—but only in developing countries. In developed countries, studies indicate that topical petrolatum ointment increases the risk of candidemia and coagulase‐negative Staphylococcus infection in the preterm population, perhaps by creating a milieu similar to occlusive dressings. For preterm infants with catheters, povidone‐iodine and chlorhexidine are comparably effective at preventing catheter colonization. Further studies are necessary to examine the safety and efficacy of various skin care interventions in premature infants with an emphasis placed on subclassifying the patient population. In the interim, it may be beneficial to develop guidelines based on the current body of evidence.

To assist with public health preparedness activities, we estimated the number of expected cases of Zika virus in Puerto Rico and associated healthcare needs. Estimated annual incidence is 3.2–5.1 times the baseline, and long-term care needs are predicted to be 3–5 times greater than in years with no Zika virus.

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