DNA Circles Research Articles

Transcriptional analysis of polydnaviral genes in the course of parasitization reveals segment‐specific patterns

Polydnaviruses are symbiotic viruses of endoparasitic wasps, which are formed in their ovary and injected along with the eggs into the host. They manipulate the host in a way to allow successful parasitoid development. A hallmark of polydnaviruses is their segmented genome consisting of several circles of double-stranded DNA. We are studying the solitary egg-larval parasitoid Chelonus inanitus (Braconidae) parasitizing Spodoptera littoralis (Noctuidae). The polydnavirus of Chelonus inanitus (CiV) protects the parasitoid larva from encapsulation by the host's immune system, slightly modifies host nutritional physiology, and induces a developmental arrest of the host in the prepupal stage. Here we present data on newly identified CiV genes and their expression patterns in the course of parasitization. None of these genes has similarity to other genes and so far no gene families could be found. A rough estimation of transcript quantities revealed that even the most highly expressed CiV genes reach maximal values, which are 250 times lower than actin. This indicates that the CiV-induced alterations of the host are brought about by a concerted action of low levels of transcripts. In an overview, we show the expression patterns of all CiV genes analysed up to now; they indicate that several genes with similar expression patterns (early, persistent, intermediate, or late) are grouped together on the same segment. This is the first observation of this type. It suggests that one function of the segmentation of the polydnavirus genome may be the grouping together of genes, which are regulated in a similar manner.

Replisome Fate upon Encountering a Leading Strand Block and Clearance from DNA by Recombination Proteins

Replication forks that collapse upon encountering a leading strand lesion are reactivated by a recombinative repair process called replication restart. Using rolling circle DNA substrates to model replication forks, we examine the fate of the helicase and both DNA polymerases when the leading strand polymerase is blocked. We find that the helicase continues over 0.5 kb but less than 3 kb and that the lagging strand DNA polymerase remains active despite its connection to a stalled leading strand enzyme. Furthermore, the blocked leading strand polymerase remains stably bound to the replication fork, implying that it must be dismantled from DNA in order for replication restart to initiate. Genetic studies have identified at least four gene products required for replication restart, RecF, RecO, RecR, and RecA. We find here that these proteins displace a stalled polymerase at a DNA template lesion. Implications of these results for replication fork collapse and recovery are discussed.

Lack of Evidence for Prolonged Double-Long Terminal Repeat Episomal HIV DNA Stability In Vivo

Lack of Evidence for Prolonged Double-Long Terminal Repeat Episomal HIV DNA Stability In Vivo

Ku80 Participates in the Targeting of Retroviral Transgenes to the Chromatin of CHO Cells

The heterodimer Ku70/80 Ku is the DNA-binding component of the DNA-PK complex required for the nonhomologous end-joining pathway. It participates in numerous nuclear processes, including telomere and chromatin structure maintenance, replication, and transcription. Ku interacts with retroviral preintegration complexes and is thought to interfere with the retroviral replication cycle, in particular the formation of 2-long terminal repeat (LTR) viral DNA circles, viral DNA integration, and transcription. We describe here the effect of Ku80 on both provirus integration and the resulting transgene expression in cells transduced with retroviral vectors. We found that transgene expression was systematically higher in Ku80-deficient xrs6 cells than in Ku80-expressing CHO cells. This higher expression was observed irrespective of the presence of the viral LTR and was also not related to the nature of the promoter. Real-time PCR monitoring of the early viral replicative steps demonstrated that the absence of Ku80 does not affect the efficiency of transduction. We analyzed the transgene distributions localization in nucleus by applying a three-dimensional reconstruction model to two-dimensional fluorescence in situ hybridization images. This indicated that the presence of Ku80 resulted in a bias toward the transgenes being located at the periphery of the nucleus associated with their being repressed; in the absence of this factor the transgenes tend to be randomly distributed and actively expressed. Therefore, although not strictly required for retroviral integration, Ku may be involved in targeting retroviral elements to chromatin domains prone to gene silencing.

Unusual Mitochondrial Genome Structures throughout the Euglenozoa

Mitochondrial DNA of Kinetoplastea is composed of different chromosomes, the maxicircle (bearing 'regular' genes) and numerous minicircles (specifying guide RNAs involved in RNA editing). In trypanosomes [Kinetoplastea], DNA circles are compacted into a single dense body, the kinetoplast. This report addresses the question whether multi-chromosome mitochondrial genomes and compacted chromosome organization are restricted to Kinetoplastea or rather occur throughout Euglenozoa, i.e., Kinetoplastea, Euglenida and Diplonemea. To this end, we investigated the diplonemid Rhynchopus euleeides and the euglenids Petalomonas cantuscygni, Peranema trichophorum and Entosiphon sulcatum, using light and electron microscopy and molecular techniques. Our findings together with previously published data show that multi-chromosome mitochondrial genomes prevail across Euglenozoa, while kinetoplast-like mtDNA packaging is confined to trypanosomes.

69. Site-Specific Genomic Integration of Lentiviral DNA Circles

69. Site-Specific Genomic Integration of Lentiviral DNA Circles

Expression of recombination-activating genes and T cell receptor gene recombination in the human T cell leukemia cell line

Recent studies have suggested that mature T cells can change their specificity through reexpression of recombination-activating genes (RAG) and RAG-mediated V(D)J recombination. This process is named receptor revision and has been observed in mature peripheral T cells from transgenic mice and human donors. However, whether thebreceptor revision in mature T cells is a random or orientated process remains poorly understood. Here we used the Jurkathuman T cell line, which represents a mature stage of T cell development, as a model to investigate the regulation of Tcell receptor (TCR) gene recombination. TCR Dbeta-Jbeta signal joint T cell receptor excision DNA circles (sjTRECs) were determined by nested and seminested PCR. Double-strand DNA breaks at recombination signal sequences (RSSs) in the TCRVbeta chain locus were detected by ligation-mediated-PCR. Further analysis of the complementarity-determining region 3 (CDR3) size of the TCRVbeta chain was examined by the TCR GeneScan technique. RAG1, RAG2, and three crucial components of the nonhomologous DNA end-joining (NHEJ) pathway were readily detected in Jurkat. Characteristics of junctional diversity of Dbeta2-Jbeta2 signal joints and ds RSS breaks associated with the Dbeta2 5' and Dbeta 2 3' sites were detected in DNA from Jurkat cells. CDR3 size and the gene sequences of the TCRVbeta chain did not change during cell proliferation. RAG1 and RAG2 and ongoing TCR gene recombination are coexpressed in Jurkat cells, but the ongoing recombination process may not play a role in modification of the TCR repertoire.However, the results suggest that Jurkat could be used as a model for studying the regulation of RAGs and V(D)J recombination and as a "special" model of the coexistence of TCR gene rearrangements and "negative" receptor revision.

Protein-induced Local DNA Bends Regulate Global Topology of Recombination Products

The tyrosine family of recombinases produces two smaller DNA circles when acting on circular DNA harboring two recombination sites in head-to-tail orientation. If the substrate is supercoiled, these circles can be unlinked or form multiply linked catenanes. The topological complexity of the products varies strongly even for similar recombination systems. This dependence has been solved here. Our computer simulation of the synapsis showed that the bend angles, ϕ, created in isolated recombination sites by protein binding before assembly of the full complex, determine the product topology. To verify the validity of this theoretical finding we measured the values of ϕ for Cre/ loxP and Flp/ FRT systems. The measurement was based on cyclization of the protein-bound short DNA fragments in solution. Despite the striking similarity of the synapses for these recombinases, action of Cre on head-to-tail target sites produces mainly unlinked circles, while that of Flp yields multiply linked catenanes. In full agreement with theoretical expectations we found that the values of ϕ for these systems are very different, close to 35° and 80°, respectively. Our findings have general implications in how small protein machines acting locally on large DNA molecules exploit statistical properties of their substrates to bring about directed global changes in topology.

Effects of lead exposure on thymic output naive T cells function

To investigate the levels of T cell receptor rearrangement excision DNA circles (TRECs) within peripheral blood from workers exposed to lead, and thereby to evaluate the number of naive T cells and recent thymic output function. Quantitative detection of TRECs in peripheral blood mononuclear cells (PBMNC) from 10 cases of workers exposed to lead was performed by real time PCR analysis. 11 workers without exposure to lead served as unexposed controls. In addition, the relationship between TRECs, age, length of service, blood lead, urea lead, blood ZPP and urea delta-ALA was investigated. The mean value of TRECs in workers exposed to lead was (2.44 +/- 1.87)/1000 PBMC, significantly under (5.60 +/- 3.96)/1000 PBMC in unexposed controls. A significant negative correlation was found between the TRECs and urea-ALA. But there was no significant correlation between them after controlling for blood lead, urea lead. Lead exposure may damage thymic output naive T cells function. Furthermore, low-level exposure to lead may damage immune system and earlier than expected.

The AAA+ protein ATAD3 has displacement loop binding properties and is involved in mitochondrial nucleoid organization

Many copies of mammalian mitochondrial DNA contain a short triple-stranded region, or displacement loop (D-loop), in the major noncoding region. In the 35 years since their discovery, no function has been assigned to mitochondrial D-loops. We purified mitochondrial nucleoprotein complexes from rat liver and identified a previously uncharacterized protein, ATAD3p. Localization studies suggested that human ATAD3 is a component of many, but not all, mitochondrial nucleoids. Gene silencing of ATAD3 by RNA interference altered the structure of mitochondrial nucleoids and led to the dissociation of mitochondrial DNA fragments held together by protein, specifically, ones containing the D-loop region. In vitro, a recombinant fragment of ATAD3p bound to supercoiled DNA molecules that contained a synthetic D-loop, with a marked preference over partially relaxed molecules with a D-loop or supercoiled DNA circles. These results suggest that mitochondrial D-loops serve to recruit ATAD3p for the purpose of forming or segregating mitochondrial nucleoids.

Production of highly knotted DNA by means of cosmid circularization inside phage capsids

BackgroundThe formation of DNA knots is common during biological transactions. Yet, functional implications of knotted DNA are not fully understood. Moreover, potential applications of DNA molecules condensed by means of knotting remain to be explored. A convenient method to produce abundant highly knotted DNA would be highly valuable for these studies.ResultsWe had previously shown that circularization of the 11.2 kb linear DNA of phage P4 inside its viral capsid generates complex knots by the effect of confinement. We demonstrate here that this mechanism is not restricted to the viral genome. We constructed DNA cosmids as small as 5 kb and introduced them inside P4 capsids. Such cosmids were then recovered as a complex mixture of highly knotted DNA circles. Over 250 μg of knotted cosmid were typically obtained from 1 liter of bacterial culture.ConclusionWith this biological system, DNA molecules of varying length and sequence can be shaped into very complex and heterogeneous knotted forms. These molecules can be produced in preparative amounts suitable for systematic studies and applications.

Detection of short repeated genomic sequences on metaphase chromosomes using padlock probes and target primed rolling circle DNA synthesis

BackgroundIn situ detection of short sequence elements in genomic DNA requires short probes with high molecular resolution and powerful specific signal amplification. Padlock probes can differentiate single base variations. Ligated padlock probes can be amplified in situ by rolling circle DNA synthesis and detected by fluorescence microscopy, thus enhancing PRINS type reactions, where localized DNA synthesis reports on the position of hybridization targets, to potentially reveal the binding of single oligonucleotide-size probe molecules. Such a system has been presented for the detection of mitochondrial DNA in fixed cells, whereas attempts to apply rolling circle detection to metaphase chromosomes have previously failed, according to the literature.MethodsSynchronized cultured cells were fixed with methanol/acetic acid to prepare chromosome spreads in teflon-coated diagnostic well-slides. Apart from the slide format and the chromosome spreading everything was done essentially according to standard protocols. Hybridization targets were detected in situ with padlock probes, which were ligated and amplified using target primed rolling circle DNA synthesis, and detected by fluorescence labeling.ResultsAn optimized protocol for the spreading of condensed metaphase chromosomes in teflon-coated diagnostic well-slides was developed. Applying this protocol we generated specimens for target primed rolling circle DNA synthesis of padlock probes recognizing a 40 nucleotide sequence in the male specific repetitive satellite I sequence (DYZ1) on the Y-chromosome and a 32 nucleotide sequence in the repetitive kringle IV domain in the apolipoprotein(a) gene positioned on the long arm of chromosome 6. These targets were detected with good efficiency, but the efficiency on other target sites was unsatisfactory.ConclusionOur aim was to test the applicability of the method used on mitochondrial DNA to the analysis of nuclear genomes, in particular as represented by metaphase spreads. An optimized protocol for chromosome spreading in diagnostic well-slides was used for the detection of circularized padlock probes amplified by target primed rolling circle DNA synthesis from condensed metaphase chromosomes. We were able to detect a 40 nucleotide sequence in the male specific repetitive satellite I sequence and a 32 nucleotide sequence in the repetitive kringle IV domain in the apolipoprotein(a) gene. Our overall conclusion is that whilst this type of reaction indeed can be brought to work on nuclear genomes, including metaphase chromosomes, the total efficiency of this multistep reaction is at present relatively low (1–10% of target sites picked up), meaning that it is best suited for the detection of targets that exist in multiple copies per cell. Changing this will require substantial efforts to systematically increase the efficiency in each step.

RNA Interference from Multimeric shRNAs Generated by Rolling Circle Transcription

Methods most commonly used for producing small interfering RNAs (siRNAs) or short hairpin RNAs (shRNAs) are chemical synthesis and intracellular expression from engineered vectors. For shRNAs, chemical synthesis is very costly and construction of vectors is laborious. Synthesis by phage RNA polymerases from their natural promoters results in a 5 -terminal triphosphate that can trigger an interferon (IFN) response. Moreover, due to the requirement of phage promoters for 5 - GPuPuPu sequences for transcription initiation, shRNA transcripts may have extra 5 -nucleotides that can constrain the sequences that can be targeted. Also, the 3 ends may have an additional n + 1 nucleotide not encoded by the template. Here we present a novel approach for synthesizing functional shRNAs via rolling circle transcription (RCT) of small (approximately 70 nt) single-stranded DNA circles using T7 RNA polymerase, which avoids these issues. Due to internal pairing, these circles are dumbbell-shaped. RCT produces large transcripts (>10 kb in length) consisting of multimers (>150 copies) of shRNAs in the absence of promoter, terminator, or primer sequences. Dumbbells targeting red fluorescent protein (DsRed), human tumor necrosis factor-alpha (TNF-alpha) and hepatitis C virus (HCV) internal ribosome entry site (IRES) were prepared and transcribed. The resulting long transcripts are substrates for Dicer. When introduced into 293FT and Huh7 cells, the multimeric transcripts inhibited their target genes at levels similar to an equivalent mass of monomeric shRNAs, indicating that they can enter the RNAi pathway. Thus, rolling circle transcription of small DNA dumbbells provides a new source of biologically active interfering RNA.

Analysis of the Recent Thymic Output Function of 23 TCR Vβ Subfamily Naïve T Cells in Patients with AML.

Regeneration of the T-cell population proceeds normally along two different pathways, in which the thymic-dependent pathway accounts for the more durable reconstitution of the T-cell compartment, and generates a more diverse TCR repertoire. Thus thymus function serves as a direct index to understand cellular immune function and potential of long-term TCR Vβ repertoire reconstitution. The complexity of TCR repertoire is generated in the thymus by regular recombination of series of gene fragments of TCR α or β chains. During these process, by-products of rearrangements are generated in the form of signal joint T-cell receptor excision DNA circles(sjTRECs), as sjTRECs are stable extrachromosomal annular DNA, are not replicated while cell dividing, and their existence suggests functional TCR generation. Thus thymic function can be evaluated by measuring sjTRECs in peripheral blood. At present, the total recent thymic output function is evaluated by quantitating δRec-ψJα sjTRECs, but it can not evaluate particular thymic emigrants of different Vα or Vβ subfamily naïve T cells. As TCR Vα and Vβ naïve T cells include many subfamilies which play different immune roles, and the complexity of TCR repertoire is an important factor for cellular immune reconstitution.Our previous studies had showed that the recent thymic output function in patients with AML was significant decrease by quantitative detection of δRec-ψJα sjTRECs. To further estimate the recent thymic emigrants of different TCR Vβ subfamily naïve T cells, this study was designed to detect the existence of 23 TCR Vβ subfamily sjTRECs in peripheral blood mononuclear cells (PBMCs) by using 23 Vβ subfamily special primers (including 2Dβ1 sense primers and 23 Vβ subfamily antisense primers). TCR 23 Vβ-Dβ 1 sjTRECs were separately amplified in genomic DNA from 5×104 and 1×104 PBMCs of samples (10 cases of normal individuals and 32 cases of the different FAB subtypes of AML patients) to estimate the frequencies of TCR 23 Vβ-Dβ1 sjTRECs by using semi-nest PCR.The results indicated that the frequencies of 23 Vβ-Dβ1 sjTRECs were different at the same cellular concentration, and the higher cellular concentration the higher frequency of Vβ subfamily sjTRECs. The number of detectable Vβ subfamily sjTRECs was (5.09±3.28) and (2.59±2.06) in 5×104 and 1×104 PBMCs from AML patients, as compared with (13.7±2.67) and (5.50±2.07) from normal individuals, and the differences were significant (both p=0.000). About 5/23(22%) of Vβ-Dβ1 sjTRECs were detected in 5×104 PBMCs from AML patients, and the frequencies of 13 Vβ subfamily sjTRECs (including Vβ1,Vββ,Vβ3,Vβ4,Vβ5, Vβ9,Vβ10,Vβ12,Vβ13,Vβ14,Vβ17,Vβ22,Vβ24-Dβ1 sjTRECs) were significantly lower than those from normal individuals, among which the lowest were Vβ10 and Vβ14-Dβ1 sjTRECs, the most frequency was Vβ21. But the difference was not significant within the different FAB subtypes of AML patients. It was negative correlation between age and the number of detectable Vβ subfamily sjTRECs in patients with AML, and patients who were < 30 years tended to be higher number of detectable Vβ subfamily sjTRECs than those ≥ 30 years, which became significant at 5×104 PBMCs level (r=−0.481, p=0.005). Taken together, the recent thymic emigrants of 23 Vβ subfamily naïve T cells were absent to a different extent or lower level among patients with AML. These results suggested that AML patients had severe cellular immunodeficiency and the capacity and potential of long-term TCR Vβ repertoire reconstitution were dramatically lowered.

The Recent Thymic Output Function Might Relate with BCR-ABL mRNA Level in Patients with CML.

Objective In order to analyze the relationship between the content of T-cell receptor excision DNA circles (TRECs) and BCR-ABL mRNA levels, evaluating the prognostic significance of thymic recent output function monitoring in patients with chronic myelogenous leukemia (CML).Methods Quantitative detection of TRECs and BCR-ABL fusion gene transcripts in peripheral blood from 15 CML patients were preformed using real-time PCR technique. And the TREC-number was related to the number of T-cells by determination of the number of CD3-positive cells. The change of BCR-ABL level in 6 CML patients was followed-up for two years.Results There was no significant correlation between TRECs and BCR-ABL mRNA in peripheral blood from CML patients at the first diagnose. Patients who had higher TRECs at diagnosis had a larger reduction of BCR-ABL level after 2 years of follow-up. While in 2 patients who underwent haemopoietic stem cell transplantation(HSCT), BCR-ABL in one patient with higher pre-transplantation TRECs value became undetectable with three consecutive detections during the first year post transplantation, but low level of BCR-ABL could be identified in the other patient.Conclusion High thymic output function in CML patients could be helpful for anti-residual CML cells.

Rad52-mediated DNA annealing after Rad51-mediated DNA strand exchange promotes second ssDNA capture

Rad51, Rad52, and RPA play central roles in homologous DNA recombination. Rad51 mediates DNA strand exchange, a key reaction in DNA recombination. Rad52 has two distinct activities: to recruit Rad51 onto single-strand (ss)DNA that is complexed with the ssDNA-binding protein, RPA, and to anneal complementary ssDNA complexed with RPA. Here, we report that Rad52 promotes annealing of the ssDNA strand that is displaced by DNA strand exchange by Rad51 and RPA, to a second ssDNA strand. An RPA that is recombination-deficient (RPA(rfa1-t11)) failed to support annealing, explaining its in vivo phenotype. Escherichia coli RecO and SSB proteins, which are functional homologues of Rad52 and RPA, also facilitated the same reaction, demonstrating its conserved nature. We also demonstrate that the two activities of Rad52, recruiting Rad51 and annealing DNA, are coordinated in DNA strand exchange and second ssDNA capture.

Direct observation of individual endogenous protein complexes in situ by proximity ligation

Cellular processes can only be understood as the dynamic interplay of molecules. There is a need for techniques to monitor interactions of endogenous proteins directly in individual cells and tissues to reveal the cellular and molecular architecture and its responses to perturbations. Here we report our adaptation of the recently developed proximity ligation method to examine the subcellular localization of protein-protein interactions at single-molecule resolution. Proximity probes-oligonucleotides attached to antibodies against the two target proteins-guided the formation of circular DNA strands when bound in close proximity. The DNA circles in turn served as templates for localized rolling-circle amplification (RCA), allowing individual interacting pairs of protein molecules to be visualized and counted in human cell lines and clinical specimens. We used this method to show specific regulation of protein-protein interactions between endogenous Myc and Max oncogenic transcription factors in response to interferon-gamma (IFN-gamma) signaling and low-molecular-weight inhibitors.

DNA Kinks Available…If Needed

In this issue of Structure , Lankas and coworkers (Lankas et al., 2006) use molecular dynamics simulations of highly strained 94 base-pair DNA circles to show DNA kinking (unstacking of base pairs). The significance of such kinks is surprisingly controversial.

Topoisomerase Action on Short DNA Duplexes Reveals Requirements for Gate and Transfer DNA Segments

Type II topoisomerases change DNA topology by passage of one DNA duplex (the transfer, T-segment) through a transient double-stranded break in another (the gate, G-segment). Here we monitor the passage between short double-stranded DNA segments within long single-stranded DNA circles that leads to catenation of the circles. To facilitate catenation, the circles were brought into close proximity using a tethering oligonucleotide, which was removed after the reaction was complete. We varied the length and the composition of the reacting DNA segments. The minimal DNA duplex length at which we detected catenation was 50-60 bp for DNA gyrase and 40 bp for topoisomerase IV (Topo IV). For Topo IV, catenation was observed when one, but not both, of the DNA-DNA duplexes was replaced by a DNA-RNA duplex. Topo IV cleaved the DNA-DNA duplex, but not the DNA-RNA duplex implying that the DNA-RNA duplex can be a T-segment but not a G-segment.

WebWatch

BioTechniquesVol. 41, No. 1 WebWatchOpen AccessWebWatchKevin AhernKevin AhernSearch for more papers by this authorPublished Online:21 May 2018https://doi.org/10.2144/000112211AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinkedInRedditEmail Encyclopedia ChloroplasticaYou're renowned experts in photosynthesis. You have a treasure trove of information and references on the topic that range from basic history, to the most complex mechanisms it employs. What do you do with all the data? Fortunately, for fans of the discipline, Drs. Orr and Govindjee answered the question by creating a massively hyperlinked web paper called Photosynthesis and the Web. The results, as they say across the Atlantic, are magnifique. Serving as an online resource, the effort fires on every cylinder, delivering a collection of links that will impress even the most jaded Internet junkie. With topics that span the range from Light Harvesting Antennas to Top Ten Reasons to Like Rubisco, Photosynthesis and the Web is a must for solar biologists.@ www.life.uiuc.edu/govindjee/photowebInvention DimensionHome to the most prestigious and lucrative prize ($500,000) given for invention, the Lemelson-MIT Program at MIT needs to be on the radar of every aspiring Edison. Named in honor of the prolific inventor, Jerome Lemelson and his wife, Dorothy, the prize recognizes inventors with a forcus on sustainable solutions to world problems. The Invention Dimension subsection takes a whimsical approach to the topic with an inventor of the week, a handbook for inventors, games/trivia, and links to other information. The most recently cited inventors include James Ferguson, the developer of liquid crystals, Dr. Sidney Pestka, a leader in research on interferons, and a student recipient, Carl Dietrich, inventor of a personal air vehicle with a range of 100–500 miles.@ web.mit.edu/invent/n-main.htmlArresting a KillerSudden oak death is devastating. Identified initially in 1995 in Marin County, California, the disease can kill the healthiest oak tree a few weeks after symptoms appear. The offending agent, Phytophthora ramorum, has caused turmoil for nurseries over the past decade, due to its ability to infect a tree years before symptoms appear and the wide collection of plants it infects—from rhododendrons to huckleberries. The agent has spread into far northern California and has most recently been found in Southern Oregon. Fighting this scourge is the California Oak Mortality Task Force with its informative Sudden Oak Death page. Maps, images, research information, a bibliographic library, educational resources, quarantine information, management recommendations, and more provide information and hope for containing and defeating this pathogen.@ www.suddenoakdeath.orgCellular Melting PotLike the descendents of an immigrant, mitochondria carry a bit of the old country with them everywhere in the form of their own genome. The 16,568 bp circle of human mitochondrial DNA exerts effects that far exceed its small size, however. Mitochondria's essential roles in oxidation and energy production are well known, of course, but the structures have been of increasing focus for cell biologists in recent years, due to the organelles' production of reactive oxygen species and their roles in the process of apoptosis. Mitomap helps track the genetic variations of this fascinating cellular resident, and through it, the relationships between genome sequence and human disease can be readily tracked.@ www.mitomap.orgNano ArchitectureNeed a blueprint for a nanostructure? You could do worse than to copy the images in The Big Picture Book of Viruses, collected by the Garry Lab at Tulane University. Viruses, arguably, the most impressive nanostructures nature has to offer, occupy front and center of this informative and educational site. The site's creator, Dr. David Sander, has done a superb job of providing easy access to content, with images/viruses arranged by name, structure/genome, host, and diseases caused. From the spiny, wheel-like appearance of the rota-viruses to the lollipop facade of the enteroviruses, every picture on the site reminds us that look are, indeed, deceiving—even the deadliest things have beauty.@ www.virology.net/Big_Virology/BVHomePage.htmlFiguresReferencesRelatedDetails Vol. 41, No. 1 Follow us on social media for the latest updates Metrics Downloaded 71 times History Published online 21 May 2018 Published in print July 2006 Information© 2006 Author(s)PDF download