Widespread Adaptive Evolution in the Human Immunodeficiency Virus Type 1 Genome

We investigated variable selective pressures among amino acid sites in HIV-1 genes. Selective pressure at the amino acid level was measured by using the nonsynonymous/synonymous substitution rate ratio ( = d_N/d_S). To identify amino acid sites under positive selection with > 1, we applied maximum likelihood models that allow variable ratios among sites to analyze genomic sequences of 26 HIV-1 lineages including subtypes A, B, and C. Likelihood ratio tests detected sites under positive selection in each of the major genes in the genome: env, gag, pol, vif, and vpr. Positive selection was also detected in nef, tat, and vpu, although those genes are very small. The majority of positive selection sites is located in gp160. Positive selection was not detected if was estimated as an average across all sites, indicating the lack of power of the averaging approach. Candidate positive selection sites were mapped onto the available protein tertiary structures and immunogenic epitopes. We measured the physiochemical properties of amino acids and found that those at positive selection sites were more diverse than those at variable sites. Furthermore, amino acid residues at exposed positive selection sites were more physiochemically diverse than at buried positive selection sites. Our results demonstrate genomewide diversifying selection acting on the HIV-1.     

The Tsetse Fly Obligate Mutualist Wigglesworthia morsitans Alters Gene Expression and Population Density via Exogenous Nutrient Provisioning

The obligate mutualist Wigglesworthia morsitans provisions nutrients to tsetse flies. The symbiont''s response to thiamine (B₁) supplementation of blood meals, specifically towards the regulation of thiamine biosynthesis and population density, is described. Despite an ancient symbiosis and associated genome tailoring, Wigglesworthia responds to nutrient availability, potentially accommodating a decreased need.     

Genome Sequence of Azotobacter vinelandii,an Obligate Aerobe Specialized To Support Diverse Anaerobic Metabolic Processes

Azotobacter vinelandii is a soil bacterium related to the Pseudomonas genus that fixes nitrogen under aerobic conditions while simultaneously protecting nitrogenase from oxygen damage. In response to carbon availability, this organism undergoes a simple differentiation process to form cysts that are resistant to drought and other physical and chemical agents. Here we report the complete genome sequence of A. vinelandii DJ, which has a single circular genome of 5,365,318 bp. In order to reconcile an obligate aerobic lifestyle with exquisitely oxygen-sensitive processes, A. vinelandii is specialized in terms of its complement of respiratory proteins. It is able to produce alginate, a polymer that further protects the organism from excess exogenous oxygen, and it has multiple duplications of alginate modification genes, which may alter alginate composition in response to oxygen availability. The genome analysis identified the chromosomal locations of the genes coding for the three known oxygen-sensitive nitrogenases, as well as genes coding for other oxygen-sensitive enzymes, such as carbon monoxide dehydrogenase and formate dehydrogenase. These findings offer new prospects for the wider application of A. vinelandii as a host for the production and characterization of oxygen-sensitive proteins.Azotobacter vinelandii is a free-living nitrogen-fixing bacterium of the gammaproteobacteria. It is found in soils worldwide, with features of nitrogen and energy metabolism relevant to agriculture (41, 42). This organism has been studied for more than 100 years by numerous scientists throughout the world. Prior to Joshua Lederberg''s discovery of sexuality in Escherichia coli (47), A. vinelandii was the experimental organism of choice for many investigators during the emergence of biochemistry as a dominant discipline within the life sciences. Examples include the classical Lineweaver-Burk kinetic parameters, developed using enzymes from A. vinelandii (51), and the isolation by Severo Ochoa of polynucleotide phosphorylase from A. vinelandii, which was used in studies that contributed to the elucidation of the genetic code (62).A. vinelandii is able to adapt its metabolism to diverse sources of nutrients. If no carbon source is present, A. vinelandii will undergo a differentiation process to form cysts that are resistant to desiccation and other chemical and physical challenges (74). While the process of encystment has been known for many years and studied at the physiological and morphological levels, there is little knowledge about the unique biosynthetic pathways that are involved and how they are regulated. Previous work has implicated the alternative sigma factors AlgU and RpoS in the differentiation process (13, 57, 64). Alginate polymers with different monomer compositions are an important structural component of the cyst, and at the end of exponential growth, A. vinelandii cells accumulate poly-beta-hydroxybutyrate (PHB) as a reserve carbon and energy source (81). The physiology of PHB formation has been well studied in a variety of different systems, and the PHB biosynthetic operon has been described (67, 77). A. vinelandii can also produce copolymers of hydroxybutyrate and hydroxyvalerate, known to improve the flexibility and stretch of bioplastics (63).A. vinelandii has long served as a model for biochemical and genetic studies of biological nitrogen fixation, the conversion of N₂ into NH₃ by a nitrogenase enzyme. The best-studied nitrogenase consists of two oxygen-sensitive metalloproteins that, in the case of the molybdenum nitrogenase, are denominated the Fe protein and the MoFe protein. A. vinelandii is unusual in that it is one of the few bacteria that contain three nitrogenases with different subunit and metal cofactor compositions, namely, the molybdenum nitrogenase, the vanadium nitrogenase, and the iron-only nitrogenase. Expression of these nitrogenases is differentially regulated by metal availability from the medium (27).Here we present the complete genome sequence of A. vinelandii DJ and discuss what the genome has revealed about the organism''s ability to protect oxygen-sensitive processes. A. vinelandii has been cited as having one of the highest respiratory rates of any known bacterium (10). Diazotrophic growth under aerobic conditions is possible because A. vinelandii can adjust oxygen consumption rates to help maintain low levels of cytoplasmic oxygen, which is otherwise detrimental not only to nitrogenase but also to other oxygen-sensitive enzymes expressed by A. vinelandii. This phenomenon is called respiratory protection. In this work, we identify unique features of the A. vinelandii genome that help to explain the coexistence of oxygen-sensitive reactions and strict aerobic metabolism. The genome sequence and annotation allowed identification of the genes involved in respiration, including key players in respiratory protection. In addition, we have identified unexpected gene clusters encoding a carbon monoxide dehydrogenase (CODH), a formate dehydrogenase (FDH), and a second hydrogenase, all of which are also oxygen-sensitive enzymes.     

Allelic Skewing of DNA Methylation Is Widespread across the Genome

DNA methylation is assumed to be complementary on both alleles across the genome, although there are exceptions, notably in regions subject to genomic imprinting. We present a genome-wide survey of the degree of allelic skewing of DNA methylation with the aim of identifying previously unreported differentially methylated regions (DMRs) associated primarily with genomic imprinting or DNA sequence variation acting in cis. We used SNP microarrays to quantitatively assess allele-specific DNA methylation (ASM) in amplicons covering 7.6% of the human genome following cleavage with a cocktail of methylation-sensitive restriction enzymes (MSREs). Selected findings were verified using bisulfite-mapping and gene-expression analyses, subsequently tested in a second tissue from the same individuals, and replicated in DNA obtained from 30 parent-child trios. Our approach detected clear examples of ASM in the vicinity of known imprinted loci, highlighting the validity of the method. In total, 2,704 (1.5%) of our 183,605 informative and stringently filtered SNPs demonstrate an average relative allele score (RAS) change ≥0.10 following MSRE digestion. In agreement with previous reports, the majority of ASM (∼90%) appears to be cis in nature, and several examples of tissue-specific ASM were identified. Our data show that ASM is a widespread phenomenon, with >35,000 such sites potentially occurring across the genome, and that a spectrum of ASM is likely, with heterogeneity between individuals and across tissues. These findings impact our understanding about the origin of individual phenotypic differences and have implications for genetic studies of complex disease.     

The Genome of Swinepox Virus

Swinepox virus (SWPV), the sole member of the Suipoxvirus genus of the Poxviridae, is the etiologic agent of a worldwide disease specific for swine. Here we report the genomic sequence of SWPV. The 146-kbp SWPV genome consists of a central coding region bounded by identical 3.7-kbp inverted terminal repeats and contains 150 putative genes. Comparison of SWPV with chordopoxviruses reveals 146 conserved genes encoding proteins involved in basic replicative functions, viral virulence, host range, and immune evasion. Notably, these include genes with similarity to genes for gamma interferon (IFN-gamma) receptor, IFN resistance protein, interleukin-18 binding protein, IFN-alpha/beta binding protein, extracellular enveloped virus host range protein, dUTPase, hydroxysteroid dehydrogenase, superoxide dismutase, serpin, herpesvirus major histocompatibility complex inhibitor, ectromelia virus macrophage host range protein, myxoma virus M011L, variola virus B22R, four ankyrin repeat proteins, three kelch-like proteins, five vaccinia virus (VV) A52R-like family proteins, and two G protein-coupled receptors. The most conserved genomic region is centrally located and corresponds to the VV region located between genes F9L and A38L. Within the terminal 13 kbp, colinearity is disrupted and multiple poxvirus gene homologues are absent or share a lower percentage of amino acid identity. Most of these differences involve genes and gene families with likely functions involving viral virulence and host range. Three open reading frames (SPV018, SPV019. and SPV020) are unique for SWPV. Phylogenetic analysis, genome organization, and amino acid identity indicate that SWPV is most closely related to the capripoxvirus lumpy skin disease virus, followed by the yatapoxvirus yaba-like disease virus and the leporipoxviruses. The gene complement of SWPV better defines Suipoxvirus within the Chordopoxvirinae subfamily and provides a basis for future genetic comparisons.     

Genome Sequencing Reveals Widespread Virulence Gene Exchange among Human Neisseria Species

Commensal bacteria comprise a large part of the microbial world, playing important roles in human development, health and disease. However, little is known about the genomic content of commensals or how related they are to their pathogenic counterparts. The genus Neisseria, containing both commensal and pathogenic species, provides an excellent opportunity to study these issues. We undertook a comprehensive sequencing and analysis of human commensal and pathogenic Neisseria genomes. Commensals have an extensive repertoire of virulence alleles, a large fraction of which has been exchanged among Neisseria species. Commensals also have the genetic capacity to donate DNA to, and take up DNA from, other Neisseria. Our findings strongly suggest that commensal Neisseria serve as reservoirs of virulence alleles, and that they engage extensively in genetic exchange.     

Complete Genome Sequence of an Infectious Bronchitis Virus Chimera between Cocirculating Heterotypic Strains

To date, multiple serotypes and genotypes of infectious bronchitis virus (IBV) have been isolated and identified. In order to provide more information on the viral evolution of IBVs, a new virulent strain named GX-NN09032, isolated from Guangxi, China, in 2009, was sequenced, and phylogenetic and recombination analyses were conducted. Furthermore, potential recombination events associated with GX-NN09032 were found in four IBV strains, including GX-YL5, DY07, CK/CH/SD09/005, TC07-2. The present study suggested that GX-NN09032 might contribute to the emergence of modern IBV variants through recombination.     

Complete Genome Sequence of an Amur Virus Isolated from Apodemus peninsulae in Northeastern China

Amur virus was recently identified as the causative agent of hemorrhagic fever with renal syndrome. Here we report the complete genome sequence of an Amur virus isolated from Apodemus peninsulae in Northeastern China. The sequence information provided here is critical for the molecular epidemiology and evolution of Amur virus in China.     

痘苗病毒基因组密码子使用频率分析

密码子使用的差别是普遍存在的现象,每一个密码子被某些生物偏爱,而在另一些生物中则很少使用.以往这方面的研究多集中在自养生物中,而对纯寄生的病毒本身及其与宿主细胞基因密码子使用频率关系的研究则很少.分析痘苗病毒哥本哈根株189个基因的密码子使用频率发现:总体上痘苗病毒偏爱使用以A/U为结尾的密码子;基因的异质性不强,没有影响密码子使用的主要趋势;在不同转录方向上和表达时相上,基因密码子使用略有不同;不同功能的基因其密码子使用上差别较大;晚期基因比早期基因与宿主密码子使用频率的差别大.上述结果表明:密码子是影响病毒和细胞相互作用、保证其自身生存的重要机制.     

Asymmetric Genome Organization in an RNA Virus Revealed via Graph-Theoretical Analysis of Tomographic Data

Cryo-electron microscopy permits 3-D structures of viral pathogens to be determined in remarkable detail. In particular, the protein containers encapsulating viral genomes have been determined to high resolution using symmetry averaging techniques that exploit the icosahedral architecture seen in many viruses. By contrast, structure determination of asymmetric components remains a challenge, and novel analysis methods are required to reveal such features and characterize their functional roles during infection. Motivated by the important, cooperative roles of viral genomes in the assembly of single-stranded RNA viruses, we have developed a new analysis method that reveals the asymmetric structural organization of viral genomes in proximity to the capsid in such viruses. The method uses geometric constraints on genome organization, formulated based on knowledge of icosahedrally-averaged reconstructions and the roles of the RNA-capsid protein contacts, to analyse cryo-electron tomographic data. We apply this method to the low-resolution tomographic data of a model virus and infer the unique asymmetric organization of its genome in contact with the protein shell of the capsid. This opens unprecedented opportunities to analyse viral genomes, revealing conserved structural features and mechanisms that can be targeted in antiviral drug design.     

Characterization of the Genome of Cytoplasmic Polyhedrosis Virus

It is possible to oxidize in situ the 3'-terminals of the double-stranded ribonucleic acid (RNA) contained in structurally intact cytoplasmic polyhedrosis virus. The number of 3'-terminals subsequently found by reduction with tritiated sodium borohydride was equivalent to the number observed in RNA first isolated from the virus and then oxidized and reduced. The viral RNA appears to occur in 10 distinct polynucleotide segments present in equimolar amounts.     

Conversion of a Chaperonin GroEL-independent Protein into an Obligate Substrate

Chaperones assist protein folding by preventing unproductive protein aggregation in the cell. In Escherichia coli, chaperonin GroEL/GroES (GroE) is the only indispensable chaperone and is absolutely required for the de novo folding of at least ∼60 proteins. We previously found that several orthologs of the obligate GroE substrates in Ureaplasma urealyticum, which lacks the groE gene in the genome, are E. coli GroE-independent folders, despite their significant sequence identities. Here, we investigated the key features that define the GroE dependence. Chimera or random mutagenesis analyses revealed that independent multiple point mutations, and even single mutations, were sufficient to confer GroE dependence on the Ureaplasma MetK. Strikingly, the GroE dependence was well correlated with the propensity to form protein aggregates during folding. The results reveal the delicate balance between GroE dependence and independence. The function of GroE to buffering the aggregation-prone mutations plays a role in maintaining higher genetic diversity of proteins.     

Photo-Assimilation of Acetate by an Obligate Phototrophic Strain of Euglena gracilis

SYNOPSIS. Light-dependent incorporation of acetate occurs in an obligate phototrophic strain of Euglena gracilis (strain L). Assimilation is into all major biochemical fractions. Acetate does not induce operation of the glyoxylate by-pass as it does in heterotrophic strains; neither does it stimulate oxygen consumption. Acetate will not replace CO₂ in phototrophic growth. A number of carbon sources tested would not support growth in the dark, and glucose was not incorporated either in the light or the dark.