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One armed PCR (OA-PCR): amplification of genomic DNA from a single primer domain.

One-armed PCR (OA-PCR) is a novel technique that allows amplification of genomic DNA from a single region of known sequence. Previously described methods are either limited to cDNA or require extensive manipulation of template prior to amplification. In OA-PCR, DNA from a small insert phage Fugu genomic library is amplified using two sequence-specific primers and a tailed vector primer. Single, specific products of between 70 bp and 1.9 kb (mean 600 bp) have been obtained following two rounds of amplification and directly sequenced without cloning. The optimum parameters have been investigated: primer pairs of 18-24 bp, separated by between 0 and 500 bp, have successfully amplified a specific product. OA-PCR represents a rapid, simple method to extend genomic sequence into noncoding and regulatory sequences. In addition, degenerate OA-PCR primer pairs have allowed cross-species amplification of novel Fugu gene homologues.

DNA, Viral↗

A bigger mouse? The rat genome unveiled.

Rattus norvegicus is an important experimental organism and interesting to evolutionary biologists. The recently published draft rat genome sequence provides us with insights into both the rat's evolution and its physiology. We learn more about genome evolution and, in particular, the adaptive significance of gene family expansions and the evolution of rodent genomes, which appears to have decelerated since the divergence of mouse and rat. An important observation is that some regions of genomes, many in noncoding regions, show very high sequence conservation, while others show unexpectedly fast evolution. Both of these may be pointers to functional significance.

Animals↗

A novel technique for in-vivo assay of viral regulatory regions in genomes of animal RNA viruses.

A novel in-vivo assay system for mapping and analyzing regulatory signals which promote transcription and expression of viral RNA genomes is described. The system was developed using infectious bursal disease virus (IBDV), a double-stranded RNA virus and Vero cells which are permissive for IBDV, as a model. The model system consisted of engineered modifications of an enhancer-less pGL3-Promoter vector such that deleted lengths of the 5' noncoding region of genome segment A of IBDV were positioned in either the plus-sense or the minus-sense orientation immediately downstream of the SV40 promoter and upstream of the luciferase (LUC) reporter gene. Transient transfections of these constructs in IBDV-infected and uninfected Vero cells resulted in endogenous generation of recombinant viral RNA-LUC containing the 5' terminal viral RNA sequences in either the plus-sense or the minus-sense orientation. LUC assays of the Vero cell lysates allowed the localization of promoter activity in the 5'-terminal 32 base pairs of genomic segment A of IBDV. Because the viral RNA transcripts produced in-vivo can be either plus-sense or minus-sense, the system can be used to assay for regulatory regions for transcription or replication for any animal RNA virus.

Animals↗

Simple sequence repeats in Escherichia coli: abundance, distribution, composition, and polymorphism.

Computer-based genome-wide screening of the DNA sequence of Escherichia coli strain K12 revealed tens of thousands of tandem simple sequence repeat (SSR) tracts, with motifs ranging from 1 to 6 nucleotides. SSRs were well distributed throughout the genome. Mononucleotide SSRs were over-represented in noncoding regions and under-represented in open reading frames (ORFs). Nucleotide composition of mono- and dinucleotide SSRs, both in ORFs and in noncoding regions, differed from that of the genomic region in which they occurred, with 93% of all mononucleotide SSRs proving to be of A or T. Computer-based analysis of the fine position of every SSR locus in the noncoding portion of the genome relative to downstream ORFs showed SSRs located in areas that could affect gene regulation. DNA sequences at 14 arbitrarily chosen SSR tracts were compared among E. coli strains. Polymorphisms of SSR copy number were observed at four of seven mononucleotide SSR tracts screened, with all polymorphisms occurring in noncoding regions. SSR polymorphism could prove important as a genome-wide source of variation, both for practical applications (including rapid detection, strain identification, and detection of loci affecting key phenotypes) and for evolutionary adaptation of microbes.

Base Composition↗

The mitochondrial genome of the olive fly Bactrocera oleae: two haplotypes from distant geographical locations.

The complete sequence of the olive fly (Bactrocera oleae) mitochondrial genome has been determined. Two independent haplotypes, from flies of distant geographical origin (Italy and Portugal) were completely sequenced. The molecule is 15815 bp long, and shows the gene content and organization typical of insects, namely thirteen protein coding genes (PCGs) encoding proteins involved in oxidative phosphorylation, two rRNAs, twenty-two tRNAs and a long (949 bp) noncoding region. The genomes of the two fly specimens share the same arrangement, differing by a mere thirty-one point mutations. The differences are mostly transitions (26) and synonymous substitutions in PCGs (21). The two new sequences are compared with others already present in the database.

Animals↗

Trends between gene content and genome size in prokaryotic species with larger genomes.

Although the evolution process and ecological benefits of symbiotic species with small genomes are well understood, these issues remain poorly elucidated for free-living species with large genomes. We have compared 115 completed prokaryotic genomes by using the Clusters of Orthologous Groups database to determine whether there are changes with genome size in the proportion of the genome attributable to particular cellular processes, because this may reflect both cellular and ecological strategies associated with genome expansion. We found that large genomes are disproportionately enriched in regulation and secondary metabolism genes and depleted in protein translation, DNA replication, cell division, and nucleotide metabolism genes compared to medium- and small-sized genomes. Furthermore, large genomes do not accumulate noncoding DNA or hypothetical ORFs, because the portion of the genome devoted to these functions remained constant with genome size. Traits other than genome size or strain-specific processes are reflected by the dispersion around the mean for cell functions that showed no correlation with genome size. For example, Archaea had significantly more genes in energy production, coenzyme metabolism, and the poorly characterized category, and fewer in cell membrane biogenesis and carbohydrate metabolism than Bacteria. The trends we noted with genome size by using Clusters of Orthologous Groups were confirmed by our independent analysis with The Institute for Genomic Research's Comprehensive Microbial Resource and Kyoto Encyclopedia of Genes and Genomes' Orthology annotation databases. These trends suggest that larger genome-sized species may dominate in environments where resources are scarce but diverse and where there is little penalty for slow growth, such as soil.

Animals↗

Viral regulatory region sequence variations in kidney tissue obtained from patients with BK virus nephropathy.

BACKGROUND: The polyomavirus genome contains a noncoding control region (NCCR), which is believed to contain the enhancer elements that are important activators of viral transcription. We hypothesized that DNA sequence variations in this region play a role in the pathogenesis of BK virus allograft nephropathy (BKVAN). METHODS: Tissue sections were prepared from 26 paraffin-embedded biopsies with BKVAN obtained from 15 patients. The sections were lysed in a proteinase K buffer and subjected to DNA sequencing using Big Dye cycle sequencing reactions run on an automated DNA sequencer (ABI 310). NCCR anatomy was compared to the genomic sequence of archetype BKV strain WW. RESULTS: Twelve putative transcription factor binding sites showed nucleotide substitutions, deletions, or duplications in at least one of the biopsies studied. Changes were most commonly found in binding sites for granulocyte/macrophage stimulating factor promoter (24/26 biopsies) and nuclear factor-I (NF-I) transcription factor (21/22 biopsies). Less frequent changes were seen at other binding sites, including T antigen (3/22 biopsies) and the cytomegalovirus immediate early (CMV IE-1) promoter (3/22 biopsies). Five biopsies showed complex rearrangements reminiscent of those described in JC virus-associated progressive multifocal leukoencephalopathy. CONCLUSION: The regulatory region of BKV shows sequence heterogeneity in biopsy tissue with viral nephropathy. Sequence variations frequently affect putative transcription factor binding sites, with potential implications for promoter activity related to genes important in viral replication. Architectural rearrangements were found in some cases but did not appear to be a prerequisite for the pathogenesis of BKVAN.

BK Virus↗

Promiscuous mitochondrial group II intron sequences in plant nuclear genomes.

Gene translocations from the organelles to the nucleus are postulated by the endosymbiont hypothesis. We here report evidence for sequence insertions in the nuclear genomes of plants that are derived from noncoding regions of the mitochondrial genome. Fragments of mitochondrial group II introns are identified in the nuclear genomes of tobacco and a bean species. The duplicated intron sequences of 75-140 bp are derived from cis- and trans-splicing introns of genes encoding subunits 1 and 5 of the NADH dehydrogenase. The mitochondrial sequences are inserted in the vicinities of a lectin gene, different glucanase genes and a gene encoding a subunit of photosystem II. Sequence similarities between the nuclear and mitochondrial copies are in the range of 80 to 97%, suggesting recent transfer events that occurred in the basic glucanase genes before and in the lectin gene after the gene duplications in the evolution of the nuclear gene families. Overlapping regions of the same introns are in two instances also involved in intramitochondrial sequence duplications.

Base Sequence↗

Differentiation-independent Activation of HPV Genome Replication by the lncRNA DINO.

Human papillomaviruses (HPV) rely on multiple host cell factors to replicate the viral genome, yet the contribution of host long noncoding RNAs (lncRNAs) to viral genome maintenance and amplification in the productive life cycle remains poorly understood. In this study, we show that the lncRNA DINO is a driver of HPV DNA replication. DINO levels increase during keratinocyte differentiation and ectopic expression of DINO promotes both HPV genome replication and the formation of replication foci, and this is independent of keratinocyte differentiation signals. Ectopic DINO expression increases select early viral transcript levels including E1^4, E1, and E2. Notably, DINO's subcellular localization is also context-dependent: during DNA damage DINO is predominantly cytoplasmic, but during keratinocyte differentiation nuclear retention is observed. This differential localization suggests that DINO has distinct functional roles in keratinocyte differentiation and HPV biology. Our findings highlight DINO as a lncRNA that promotes HPV genome replication and suggest that lncRNAs may play underappreciated roles in host-virus interactions. This work provides a foundation for further exploration of lncRNAs as potential therapeutic targets in HPV-associated diseases.

Journal Article↗

What controls the length of noncoding DNA?

Several recent studies of genome evolution indicate that the rate of DNA loss exceeds that of DNA gain, leading to an underlying mutational pressure towards collapsing the length of noncoding DNA. That such a collapse is not observed suggests opposing mechanisms favoring longer noncoding regions. The presence of transposable elements alone also does not explain observed features of noncoding DNA. At present, a multidisciplinary approach--using population genetics techniques, large-scale genomic analyses, and in silico evolution--is beginning to provide new and valuable insights into the forces that shape the length of noncoding DNA and, ultimately, genome size. Recombination, in a broad sense, might be the missing key parameter for understanding the observed variation in length of noncoding DNA in eukaryotes.

Animals↗

Deterministic mutation rate variation in the human genome.

Several studies of substitution rate variation have indicated that the local mutation rate varies over the mammalian genome. In the present study, we show significant variation in substitution rates within the noncoding part of the human genome using 4.7 Mb of human-chimpanzee pairwise comparisons. Moreover, we find a significant positive covariation of lineage-specific chimpanzee and human local substitution rates, and very similar mean substitution rates down the two lineages. The substitution rate variation is probably not caused by selection or biased gene conversion, and so we conclude that mutation rates vary deterministically across the noncoding nonrepetitive regions of the human genome. We also show that noncoding substitution rates are significantly affected by G+C base composition, partly because the base composition is not at equilibrium.

Amino Acid Substitution↗

Evolution of noncoding and silent coding sites in the Plasmodium falciparum and Plasmodium reichenowi genomes.

We compared levels of sequence divergence between fourfold synonymous coding sites and noncoding sites from the intergenic and intronic regions of the Plasmodium falciparum and Plasmodium reichenowi genomes. We observed significant differences in the level of divergence between these classes of silent sites. Fourfold synonymous coding sites exhibited the highest level of sequence divergence, followed by introns, and then intergenic sequences. This pattern of relative divergence rates has been observed in primate genomes but was unexpected in Plasmodium due to a paucity of variation at silent sites in P. falciparum and the corollary hypothesis that silent sites in this genome may be subject to atypical selective constraints. Exclusion of hypermutable CpG dinucleotides reduces the divergence level of synonymous coding sites to that of intergenic sites but does not diminish the significantly higher divergence level of introns relative to intergenic sites. A greater than expected incidence of CpG dinucleotides in intergenic regions less than 500 bp from genes may indicate selective maintenance of regulatory motifs containing CpGs. Divergence rates of different classes of silent sites in these Plasmodium genomes are determined by a combination of mutational and selective pressures.

Animals↗

Mutation of hMSH3 and hMSH6 mismatch repair genes in genetically unstable human colorectal and gastric carcinomas.

Mutations within microsatellite sequences, consisting of additions or deletions of repeat units, are known as the replication/repair error positive (RER+) phenotype or micorsatellite instability (MI). Microsatellite instability has been demonstrated in hereditary and sporadic colorectal carcinomas and is usually observed in noncoding regions of genomic DNA. However, relatively few coding region targets of MI have been identified thus far. Using PCR, we amplified regions encompassing (A)8 and (C)8 microsatellite tracts within hMSH3 and hMSH6 from 31 RER+ sporadic colorectal tumors, 8 hereditary colon cancers, 23 RER+ gastric carcinomas, and 32 RER- gastric tumors. Mutations were found in 11 (36%) of 31 sporadic colon carcinomas, 4 (50%) of 8 hereditary colorectal cancers, and 5 (22%) of 23 RER+ gastric carcinomas, but in only 2 (6%) of 32 RER- gastric carcinomas. These frameshift mutations cause premature stop codons downstream that are predicted to abolish normal protein function. Our results and those of others suggest that DNA mismatch repair genes, such as hMSH3 and hMSH6, are targets for the mutagenic activity of upstream mismatch repair gene mutations and that this enhanced genomic instability may accelerate the accumulation of mutations in RER+ tumors.

Adenocarcinoma↗

Strategy for construction of live picornavirus vaccines.

A number of recombinant viruses between the virulent Mahoney and the attenuated Sabin 1 strains of type 1 poliovirus were constructed in vitro using their infectious cDNA clones. Monkey neurovirulence tests on these recombinant viruses revealed that the surface structure of the virion particle had a little correlation with the neurovirulent phenotype, and that the strong neurovirulence determinant(s) resided in the 5' noncoding sequence. These results in turn led to two possible strategies for constructing live attenuated picornavirus strains. One is to use the Sabin 1 strain as a vector carrying foreign antigenicities. The other is the construction of the attenuated picornaviruses by introducing mutations into the 5' noncoding sequences. The antigenicity of the Sabin 1 strain was successfully changed to those of other poliovirus serotypes without loss of vaccine quality. Furthermore, it was proved that introduction of deletion mutation into the 5' noncoding sequence of genomes of the Sabin 1 and Mahoney strains resulted in construction of viruses with a less neurovirulent phenotype.

Chromosome Deletion↗

A human gene, ATP6E1, encoding a testis-specific isoform of H(+)-ATPase subunit E.

We have identified a novel human gene, ATP6E, encoding an E subunit isoform of vacuolar-type proton-translocating ATPase (V-ATPase). ATP6E1 was mapped to approximately 2p16-p12 on chromosome 2, and has a simple genomic organization: a noncoding exon and a coding one for an E1 isoform separated by a 6.1 kb intron, with boundaries following the GT-AG rule. Transcription initiation sites were found at -375 and -158 bases upstream of the translation initiation codon. Northern blotting analysis demonstrated that ATP6E1 is specifically transcribed in testis as 1.1 kb and 2.2 kb mRNAs, whereas the previously reported ATP6E2 (E2) is expressed in all tissues tested. E1 exhibited 76.9% identity with ubiquitously expressed E2, and both isoforms functionally complemented null mutations of the yeast counterpart VMA4, indicating that they are bona fide subunits of the V-ATPase complex.

Amino Acid Sequence↗

Usefulness of nested PCR and sequence analysis in a nosocomial outbreak of neonatal enterovirus infection.

BACKGROUND: Non-polio enterovirus infections are recognized in children during summer-fall seasons and they sometimes cause large outbreaks. We experienced a nosocomial infection in the neonatal nursery and echovirus type 7 was isolated from samples of four patients. OBJECTIVES: We diagnosed the horizontal infection of four neonates by reverse transcriptase-nested polymerase chain reaction (RT-nested PCR) and the nucleotide sequence. STUDY DESIGN: Total RNA was extracted from clinical isolates, serum samples and cerebrospinal fluid (CSF). We amplified enterovirus genome in the 5'-noncoding region by nested PCR and determined the nucleotide sequences. RESULTS: Enterovirus genome was detected in all isolates, in the acute-phase sera in all four patients and in the CSF in one patient by the first PCR. By using nested PCR, the genome was detected from convalescent-phase sera in two patients. All enterovirus genome obtained from the nursery outbreak showed the same sequences with 100% homology. CONCLUSION: We demonstrated the clinical advantages of RT-nested PCR from serum samples and the analysis of nucleotide sequencing gave the supportive evidence of identification of transmission pathway.

5' Untranslated Regions↗

Genomic regions of neurovirulence and attenuation in Theiler murine encephalomyelitis virus.

Full-length cDNA clones of two Theiler murine encephalomyelitis virus (TMEV) strains, one highly virulent and the other less virulent, were constructed in the bacterial plasmid pGEMR-3. Transfection of BHK-21 cells with RNA transcribed from these cDNAs yielded progeny viruses with the exact in vitro growth phenotype and mouse neurovirulence pattern of the respective parental virus strains. RNA transcripts derived from recombinant chimeras constructed by exchanging corresponding genomic regions [5' noncoding, leader/P1 (L/P1), P2, P3, and 3' noncoding] between the parental cDNAs were infectious and enabled analysis of the growth characteristics in vitro and mouse neurovirulence of the chimeras. A correlation was found between plaque size and temperature sensitivity and the origin of the L/P1 region. Neurovirulence mapped primarily to the L/P1 region encoding the leader and coat proteins. Depending on parental origin, the 5' noncoding region either influenced virus attenuation or augmented virulence.

Animals↗

Presence and distribution of human papillomavirus sense and antisense RNA transcripts in genital cancers.

RNA transcription in eight human papillomavirus (HPV) type 16-positive genital carcinomas and in two cervical squamous cell carcinoma (SCC)-derived cell lines was analysed by in situ hybridization using 125I-labelled subgenomic riboprobes. Transcripts corresponding to the E6 and E7 open reading frames were always present, except within the keratinizing layers of differentiated SCCs. Intranuclear E1 gene transcripts were detectable in both cell lines and some tumours whereas E2/E4 transcripts were absent from five of seven assessable tumours, suggesting transcription from integrated viral DNA. When mRNA sense riboprobes were used as controls, no signal was seen in the two cell lines; however, three tumours contained a focal, intense nuclear RNase-sensitive signal using mRNA sense riboprobes. This antisense RNA signal mapped across the whole genome including the noncoding region. In one tumour, the presence of antisense RNA was independently confirmed by using E7 and E2/E4 RNA probes of both orientations in RNase protection assays. Transcription of antisense RNA may be a natural feature of some HPV-positive genital tumours and its possible role in modulating cell behaviour in vivo requires further investigation.

Carcinoma, Squamous Cell↗