HIV/AIDS in Asia： The Shape of Epidemics and Their Molecular Epidemiology

The Asia-Pacific region is a home to 60% of the population in the world and to approximately one quarter of people with HIV/AIDS. Close to a million of people has been infected and a half million people died of AIDS annually in Asia,becoming the second largest epicenter of global AIDS epidemic. Molecular epidemiology has been useful tool to track a course of HIV spread. In-depth knowledge from the studies on molecular epidemiology elucidates the dynamics of HIV spread and the interrelationship of epidemics in the different regions in Asia.     

Structural basis of the initial binding of tRNA(Ile) lysidine synthetase TilS with ATP and L-lysine

In the bacterial genetic-code system, the codon AUA is decoded as isoleucine by tRNA(Ile)(2) with the lysidine residue at the wobble position. Lysidine is derived from cytidine, with ATP and L-lysine, by tRNA(Ile) lysidine synthetase (TilS), which is an N-type ATP pyrophosphatase. In this study, we determined the crystal structure of Aquifex aeolicus TilS, complexed with ATP, Mg2+, and L-lysine, at 2.5 A resolution. The presence of the TilS-specific subdomain causes the active site to have two separate gateways, a large hole and a narrow tunnel on the opposite side. ATP is bound inside the hole, and L-lysine is bound at the entrance of the tunnel. The conserved Asp36 in the PP-motif coordinates Mg2+. In these initial binding modes, the ATP, Mg2+, and L-lysine are held far apart from each other, but they seem to be brought together for the reaction upon cytidine binding, with putative structural changes of the complex.     

Molecular characterization of T4-type bacteriophages in a rice field

Bacteriophages, the viruses that infect bacteria, are the most abundant biological entities in the biosphere and play a key role in global biogeochemical cycling. All T4-type bacteriophage isolates tested so far have a conserved genetic module that encodes the virion components including gene 23 (g23), the major capsid protein. Molecular analysis of the g23 sequence revealed a remarkable level of diversity of T4-type bacteriophages isolated from rice straw and surface soil in a Japanese rice field. It was found that g23 sequences obtained from the rice field were quite distinctive from those obtained in marine environments. Phylogenetic analysis showed that most of these g23 sequences belonged to two novel subgroups of T4-type bacteriophages, although some of them were related to well-studied subgroups of T4-type bacteriophages, such as marine cyanophage isolates of exoT-evens.     

Small‐molecule auxin inhibitors that target YUCCA are powerful tools for studying auxin function

Auxin is essential for plant growth and development, this makes it difficult to study the biological function of auxin using auxin‐deficient mutants. Chemical genetics have the potential to overcome this difficulty by temporally reducing the auxin function using inhibitors. Recently, the indole‐3‐pyruvate (IPyA) pathway was suggested to be a major biosynthesis pathway in Arabidopsis thaliana L. for indole‐3‐acetic acid (IAA), the most common member of the auxin family. In this pathway, YUCCA, a flavin‐containing monooxygenase (YUC), catalyzes the last step of conversion from IPyA to IAA. In this study, we screened effective inhibitors, 4‐biphenylboronic acid (BBo) and 4‐phenoxyphenylboronic acid (PPBo), which target YUC. These compounds inhibited the activity of recombinant YUC in vitro, reduced endogenous IAA content, and inhibited primary root elongation and lateral root formation in wild‐type Arabidopsis seedlings. Co‐treatment with IAA reduced the inhibitory effects. Kinetic studies of BBo and PPBo showed that they are competitive inhibitors of the substrate IPyA. Inhibition constants (K_i) of BBo and PPBo were 67 and 56 nm , respectively. In addition, PPBo did not interfere with the auxin response of auxin‐marker genes when it was co‐treated with IAA, suggesting that PPBo is not an inhibitor of auxin sensing or signaling. We propose that these compounds are a class of auxin biosynthesis inhibitors that target YUC. These small molecules are powerful tools for the chemical genetic analysis of auxin function.     

Intramolecular Binding of the Rad9 C Terminus in the Checkpoint Clamp Rad9-Hus1-Rad1 Is Closely Linked with Its DNA Binding

The human checkpoint clamp Rad9-Hus1-Rad1 (9-1-1) is loaded onto chromatin by its loader complex, Rad17-RFC, following DNA damage. The 120-amino acid (aa) stretch of the Rad9 C terminus (C-tail) is unstructured and projects from the core ring structure (CRS). Recent studies showed that 9-1-1 and CRS bind DNA independently of Rad17-RFC. The DNA-binding affinity of mutant 9^ΔC-1-1, which lacked the Rad9 C-tail, was much higher than that of wild-type 9-1-1, suggesting that 9-1-1 has intrinsic DNA binding activity that manifests in the absence of the C-tail. C-tail added in trans interacted with CRS and prevented it from binding to DNA. We narrowed down the amino acid sequence in the C-tail necessary for CRS binding to a 15-aa stretch harboring two conserved consecutive phenylalanine residues. We prepared 9-1-1 mutants containing the variant C-tail deficient for CRS binding, and we demonstrated that the mutant form restored DNA binding as efficiently as 9^ΔC-1-1. Furthermore, we mapped the sequence necessary for TopBP1 binding within the same 15-aa stretch, demonstrating that TopBP1 and CRS share the same binding region in the C-tail. Indeed, we observed their competitive binding to the C-tail with purified proteins. The importance of interaction between 9-1-1 and TopBP1 for DNA damage signaling suggests that the competitive interactions of TopBP1 and CRS with the C-tail will be crucial for the activation mechanism.     

A deletion in a cis element of Foxe3 causes cataracts and microphthalmia in rct mice

The Rinshoken cataract (rct) mutation, which causes congenital cataracts, is a recessive mutation found in SJL/J mice. All mutants present with opacity in the lens by 2?months of age. The rct locus was mapped to a 1.6-Mb region in Chr 4 that contains the Foxe3 gene. This gene is responsible for cataracts in humans and mice, and it plays a crucial role in the development of the lens. Furthermore, mutation of Foxe3 causes various ocular defects. We sequenced the genomic region of Foxe3, including the coding exons and UTRs; however, no mutations were discovered in these regions. Because there were no differences in Foxe3 sequences between the rct/rct and wild-type mice, we inferred that a mutation was located in the regulatory regions of the Foxe3 gene. To test this possibility, we sequenced a 5' noncoding region that is highly conserved among vertebrates and is predicted to be the major enhancer of Foxe3. This analysis revealed a deletion of 22-bp located approximately 3.2-kb upstream of the start codon of Foxe3 in rct mice. Moreover, we demonstrated by RT-PCR and in situ hybridization that the rct mutant has reduced expression of Foxe3 in the lens during development. We therefore suggest that cataracts in rct mice are caused by reduced Foxe3 expression in the lens and that this decreased expression is a result of a deletion in a cis-acting regulatory element.     

The effect of highly active antiretroviral therapy on the survival of HIV-infected children in a resource-deprived setting: a cohort study

Background

The effect of highly active antiretroviral therapy (HAART) on the survival of HIV-infected children has not been well quantified. Because most pediatric HIV occurs in low- and middle-income countries, our objective was to provide a first estimate of this effect among children living in a resource-deprived setting.

Methods and Findings

Observational data from HAART-naïve children enrolled into an HIV care and treatment program in Kinshasa, Democratic Republic of the Congo, between December 2004 and May 2010 were analyzed. We used marginal structural models to estimate the effect of HAART on survival while accounting for time-dependent confounders affected by exposure. At the start of follow-up, the median age of the 790 children was 5.9 y, 528 (66.8%) had advanced or severe immunodeficiency, and 405 (51.3%) were in HIV clinical stage 3 or 4. The children were observed for a median of 31.2 mo and contributed a total of 2,089.8 person-years. Eighty children (10.1%) died, 619 (78.4%) initiated HAART, six (0.8%) transferred to a different care provider, and 76 (9.6%) were lost to follow-up. The mortality rate was 3.2 deaths per 100 person-years (95% confidence interval [CI] 2.4–4.2) during receipt of HAART and 6.0 deaths per 100 person-years (95% CI 4.1–8.6) during receipt of primary HIV care only. The mortality hazard ratio comparing HAART with no HAART from a marginal structural model was 0.25 (95% CI 0.06–0.95).

Conclusions

HAART reduced the hazard of mortality in HIV-infected children in Kinshasa by 75%, an estimate that is similar in magnitude but with lower precision than the reported effect of HAART on survival among children in the United States. Please see later in the article for the Editors'' Summary     

Detecting drug-resistant tuberculosis: the importance of rapid testing

Despite numerous intervention strategies, including the direct observed short-course treatment strategy and improved diagnostic methods, the incidence of multidrug-resistant and extensively drug-resistant tuberculosis (TB) continues to rise globally. Many treatment policies are based on the model that acquisition of drug resistance in already infected individuals drives the drug-resistant TB epidemic, hence the focus on drug-resistance testing of retreatment cases. However, molecular epidemiology and mathematical modeling suggest that the majority of multidrug-resistant TB cases are due to ongoing transmission of multidrug-resistant strains. This is most likely the result of diagnostic delay, thereby emphasizing the need for rapid diagnostics and comprehensive contact tracing, as well as active case finding. Current diagnosis of TB in low-income, high-burden regions relies on smear microscopy and clinical signs and symptoms. However, this smear-centered approach has many pitfalls, including low sensitivity in HIV patients and children, the inability of smear to reveal drug-resistance patterns, and the need for sampling on consecutive days. In order to address these limitations, efforts have been made to expand access to Mycobacterium tuberculosis culture and drug susceptibility testing. However, the slow growth rate of the causative agent, M. tuberculosis, contributes to significant diagnostic delay. Molecular-based diagnostic methods, targeting mutations that are known to confirm drug resistance, are capable of significantly reducing diagnostic delay. Two such methods, the line-probe assay and the real-time PCR-based Xpert? MTB/RIF assay, have been described. The latter test shows particular promise for smear-negative and extrapulmonary specimens. This may prove especially useful in settings where co-infection rates with HIV are high. However, since most research focuses on the performance of both of these assays, further investigations need to be done regarding the impact of the routine implementation of these assays on TB control programs and the cost effectiveness thereof.