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  • Journal article
    Duncan SM, Carbajo CG, Nagar R, Zhong Q, Breen C, Ferguson MAJ, Tiengwe Cet al., 2024,

    Generation of a bloodstream form Trypanosoma brucei double glycosyltransferase null mutant competent in receptor-mediated endocytosis of transferrin.

    , PLoS Pathog, Vol: 20

    The bloodstream form of Trypanosoma brucei expresses large poly-N-acetyllactosamine (pNAL) chains on complex N-glycans of a subset of glycoproteins. It has been hypothesised that pNAL may be required for receptor-mediated endocytosis. African trypanosomes contain a unique family of glycosyltransferases, the GT67 family. Two of these, TbGT10 and TbGT8, have been shown to be involved in pNAL biosynthesis in bloodstream form Trypanosoma brucei, raising the possibility that deleting both enzymes simultaneously might abolish pNAL biosynthesis and provide clues to pNAL function and/or essentiality. In this paper, we describe the creation of a TbGT10 null mutant containing a single TbGT8 allele that can be excised upon the addition of rapamycin and, from that, a TbGT10 and TbGT8 double null mutant. These mutants were analysed by lectin blotting, glycopeptide methylation linkage analysis and flow cytometry. The data show that the mutants are defective, but not abrogated, in pNAL synthesis, suggesting that other GT67 family members can compensate to some degree for loss of TbGT10 and TbGT8. Despite there being residual pNAL synthesis in these mutants, certain glycoproteins appear to be particularly affected. These include the lysosomal CBP1B serine carboxypeptidase, cell surface ESAG2 and the ESAG6 subunit of the essential parasite transferrin receptor (TfR). The pNAL deficient TfR in the mutants continued to function normally with respect to protein stability, transferrin binding, receptor mediated endocytosis of transferrin and subcellular localisation. Further the pNAL deficient mutants were as viable as wild type parasites in vitro and in in vivo mouse infection experiments. Although we were able to reproduce the inhibition of transferrin uptake with high concentrations of pNAL structural analogues (N-acetylchito-oligosaccharides), this effect disappeared at lower concentrations that still inhibited tomato lectin uptake, i.e., at concentrations able to outcompete lectin-
  • Journal article
    Budzak J, Goodwin I, Tiengwe C, Rudenko Get al., 2023,

    Imaging of genomic loci in Trypanosoma brucei using an optimised LacO-LacI system

    , Molecular and Biochemical Parasitology, Vol: 256, ISSN: 0166-6851

    Visualisation of genomic loci by microscopy is essential for understanding nuclear organisation, particularly at the single cell level. One powerful technique for studying the positioning of genomic loci is through the Lac Operator-Lac Repressor (LacO-LacI) system, in which LacO repeats introduced into a specific genomic locus can be visualised through expression of a LacI-protein fused to a fluorescent tag. First utilised in Trypanosoma brucei over 20 years ago, we have now optimised this system with short, stabilised LacO repeats of less than 2 kb paired with a constitutively expressed mNeongreen::LacI fusion protein to facilitate visualisation of genomic loci. We demonstrate the compatibility of this system with super-resolution microscopy and propose its suitability for multiplexing with inducible RNAi or protein over expression which will allow analysis of nuclear organisation after perturbation of gene expression.
  • Conference paper
    Moore C, Gwira TM, Tiengwe C, Yamthe Let al., 2023,

    In vitro antiproliferative synergism of phenolic compounds and Glucantime<SUP>®</SUP> against <i>Leishmania donovani</i>

    , Publisher: WILEY, Pages: 84-85, ISSN: 1360-2276
  • Journal article
    Wincott CJ, Sritharan G, Benns HJ, May D, Gilabert-Carbajo C, Bunyan M, Fairweather AR, Alves E, Andrew I, Game L, Frickel E-M, Tiengwe C, Ewald SE, Child MAet al., 2022,

    Cellular barcoding of protozoan pathogens reveals the within-host population dynamics of Toxoplasma gondii host colonization

    , Cell Reports Methods, Vol: 2, Pages: 1-16, ISSN: 2667-2375

    Cellular barcoding techniques are powerful tools to understand microbial pathogenesis. However, barcoding strategies have not been broadly applied to protozoan parasites, which have unique genomic structures and virulence strategies compared with viral and bacterial pathogens. Here, we present a CRISPR-based method to barcode protozoa, which we successfully apply to Toxoplasma gondii and Trypanosoma brucei. Using libraries of barcoded T. gondii, we evaluate shifts in the population structure from acute to chronic infection of mice. Contrary to expectation, most barcodes were present in the brain one month post-intraperitoneal infection in both inbred CBA/J and outbred Swiss mice. Although parasite cyst number and barcode diversity declined over time, barcodes representing a minor fraction of the inoculum could become a dominant population in the brain by three months post-infection. These data establish a cellular barcoding approach for protozoa and evidence that the blood-brain barrier is not a major bottleneck to colonization by T. gondii.
  • Journal article
    Gilabert Carbajo C, Cornell LJ, Madbouly Y, Lai Z, Yates PA, Tinti M, Tiengwe Cet al., 2021,

    Novel aspects of iron homeostasis in pathogenic bloodstream form Trypanosoma brucei.

    , PLoS Pathogens, Vol: 17, Pages: 1-34, ISSN: 1553-7366

    Iron is an essential regulatory signal for virulence factors in many pathogens. Mammals and bloodstream form (BSF) Trypanosoma brucei obtain iron by receptor-mediated endocytosis of transferrin bound to receptors (TfR) but the mechanisms by which T. brucei subsequently handles iron remains enigmatic. Here, we analyse the transcriptome of T. brucei cultured in iron-rich and iron-poor conditions. We show that adaptation to iron-deprivation induces upregulation of TfR, a cohort of parasite-specific genes (ESAG3, PAGS), genes involved in glucose uptake and glycolysis (THT1 and hexokinase), endocytosis (Phosphatidic Acid Phosphatase, PAP2), and most notably a divergent RNA binding protein RBP5, indicative of a non-canonical mechanism for regulating intracellular iron levels. We show that cells depleted of TfR by RNA silencing import free iron as a compensatory survival strategy. The TfR and RBP5 iron response are reversible by genetic complementation, the response kinetics are similar, but the regulatory mechanisms are distinct. Increased TfR protein is due to increased mRNA. Increased RBP5 expression, however, occurs by a post-transcriptional feedback mechanism whereby RBP5 interacts with its own, and with PAP2 mRNAs. Further observations suggest that increased RBP5 expression in iron-deprived cells has a maximum threshold as ectopic overexpression above this threshold disrupts normal cell cycle progression resulting in an accumulation of anucleate cells and cells in G2/M phase. This phenotype is not observed with overexpression of RPB5 containing a point mutation (F61A) in its single RNA Recognition Motif. Our experiments shed new light on how T. brucei BSFs reorganise their transcriptome to deal with iron stress revealing the first iron responsive RNA binding protein that is co-regulated with TfR, is important for cell viability and iron homeostasis; two essential processes for successful proliferation.
  • Working paper
    Carbajo CG, Cornell LJ, Madbouly Y, Lai Z, Yates PA, Tinti M, Tiengwe Cet al., 2021,

    Novel aspects of iron homeostasis in pathogenic bloodstream form <i>Trypanosoma brucei</i>

    <jats:title>Abstract</jats:title><jats:p>Iron is an essential regulatory signal for virulence factors in many pathogens. Mammals and bloodstream form (BSF) <jats:italic>Trypanosoma brucei</jats:italic> obtain iron by receptor-mediated endocytosis of transferrin bound to receptors (TfR) but the mechanisms by which <jats:italic>T. brucei</jats:italic> subsequently handles iron remains enigmatic. Here, we analyse the transcriptome of <jats:italic>T. brucei</jats:italic> cultured in iron-rich and iron-poor conditions. We show that adaptation to iron-deprivation induces upregulation of TfR, a cohort of parasite-specific genes (ESAG3, PAGS), genes involved in glucose uptake and glycolysis (THT1 and hexokinase), endocytosis (Phosphatidic Acid Phosphatase, PAP2), and most notably a divergent RNA binding protein RBP5, indicative of a non-canonical mechanism for regulating intracellular iron levels. We show that cells depleted of TfR by RNA silencing import free iron as a compensatory survival strategy. The TfR and RBP5 iron response are reversible by genetic complementation, the response kinetics are similar, but the regulatory mechanisms are distinct. Increased TfR protein is due to increased mRNA. Increased RBP5 expression, however, occurs by a post-transcriptional feedback mechanism whereby RBP5 interacts with its own, and with <jats:italic>PAP2</jats:italic> mRNAs. Further observations suggest that increased RBP5 expression in iron-deprived cells has a maximum threshold as ectopic overexpression above this threshold disrupts normal cell cycle progression resulting in an accumulation of anucleate cells and cells in G2/M phase. This phenotype is not observed with overexpression of RPB5 containing a point mutation (F61A) in its single RNA Recognition Motif. Our experiments shed new light on how <jats:italic>T. brucei</jats:italic> BSFs reorganise their transcriptome to deal with iron stress reveal
  • Working paper
    Wincott CJ, Sritharan G, Benns HJ, Liakath FB, Gilabert-Carbajo C, Bunyan M, Fairweather AR, Alves E, Andrew I, Game L, Frickel EM, Tiengwe C, Ewald SE, Child MAet al., 2020,

    Cellular barcoding of protozoan pathogens reveals the within-host population dynamics of<i>Toxoplasma gondii</i>host colonization

    <jats:title>Abstract</jats:title><jats:p>Molecular barcoding techniques have emerged as powerful tools to understand microbial pathogenesis. However, barcoding strategies have not been extended to protozoan parasites, which have unique genomic structures and virulence strategies compared to viral and bacterial pathogens. Here, we present a versatile CRISPR-based method to barcode protozoa, which we successfully apply to<jats:italic>Toxoplasma gondii</jats:italic>and<jats:italic>Trypanosoma brucei</jats:italic>. The murine brain is an important transmission niche for<jats:italic>T. gondii</jats:italic>, and brain persistence is a clinically untreatable feature of infection. The blood-brain barrier is expected to physically restrict parasite colonization of this niche, resulting in a selection bottleneck. Using libraries of barcoded<jats:italic>T. gondii</jats:italic>we evaluate shifts in the population structure from acute to chronic infection of mice. Contrary to expectation, most barcodes were present in the brain one-month post-intraperitoneal infection in both inbred CBA/J and outbred Swiss mice. Although parasite cyst number and barcode diversity declined over time, barcodes that represented a minor fraction of the inoculum could become a dominant population in the brain by three months post-infection. Together, these data establish the first, robust molecular barcoding approach for protozoa and evidence that the blood-brain barrier does not represent a major bottleneck to colonization by<jats:italic>T. gondii</jats:italic>.</jats:p>
  • Journal article
    Koeller CM, Tiengwe C, Schwartz KJ, Bangs JDet al., 2020,

    Steric constraints control processing of glycosylphosphatidylinositol anchors in <i>Trypanosoma brucei</i>

    , JOURNAL OF BIOLOGICAL CHEMISTRY, Vol: 295, Pages: 2227-2238, ISSN: 0021-9258
  • Journal article
    Tiengwe C, 2019,

    mSphere of influence: modifying an old method to study RNA-protein interactions

    , mSphere, Vol: 4, Pages: 1-2, ISSN: 2379-5042

    Calvin Tiengwe works on posttranscriptional gene regulation and iron homeostasis in the parasitic protozoan Trypanosoma brucei. In this mSphere of Influence article, he reflects on how the paper “Comprehensive identification of RNA-protein interactions in any organism using orthogonal organic phase separation (OOPS)” by Queiroz et al. (Nat Biotechnol 37:169–178, 2019, https://doi.org/10.1038/s41587-018-0001-2) influenced his research by providing a tool to capture RNA-protein complexes on a global scale using acid guanidinium thiocyanate-phenol-chloroform (AGPC), an old method hitherto applied for RNA, DNA, or protein purification.
  • Journal article
    Tiengwe CW, Koeller C, Bangs J, 2018,

    ER-associated degradation and disposal of misfolded GPI-anchored proteins in Trypanosoma brucei

    , Molecular Biology of the Cell, Vol: 29, Pages: 2359-2507, ISSN: 1059-1524

    Misfolded secretory proteins are retained by endoplasmic reticulum quality control (ERQC) and degraded in the proteasome by ER-associated degradation (ERAD). However, in yeast and mammals, misfolded glycosylphosphatidylinositol (GPI)-anchored proteins are preferentially degraded in the vacuole/lysosome. We investigate this process in the divergent eukaryotic pathogen Trypanosoma brucei using a misfolded GPI-anchored subunit (HA:E6) of the trypanosome transferrin receptor. HA:E6 is N-glycosylated and GPI-anchored and accumulates in the ER as aggregates. Treatment with MG132, a proteasome inhibitor, generates a smaller protected polypeptide (HA:E6*), consistent with turnover in the proteasome. HA:E6* partitions between membrane and cytosol fractions, and both pools are proteinase K-sensitive, indicating cytosolic disposition of membrane-associated HA:E6*. HA:E6* is de-N-glycosylated and has a full GPI-glycan structure from which dimyristoylglycerol has been removed, indicating that complete GPI removal is not a prerequisite for proteasomal degradation. However, HA:E6* is apparently not ubiquitin-modified. The trypanosome GPI anchor is a forward trafficking signal; thus the dynamic tension between ERQC and ER exit favors degradation by ERAD. These results differ markedly from the standard eukaryotic model systems and may indicate an evolutionary advantage related to pathogenesis.
  • Journal article
    Tiengwe C, Bush PJ, Bangs JD, 2017,

    Controlling transferrin receptor trafficking with GPI-valence in bloodstream stage African trypanosomes

    , PLoS Pathogens, Vol: 13, Pages: 1-24, ISSN: 1553-7366

    Bloodstream-formAfricantrypanosomesencodetwostructurallyrelatedglycosylphosphati-dylinositol(GPI)-anchoredproteinsthatarecriticalvirulencefactors,variantsurfaceglyco-protein(VSG)forantigenicvariationandtransferrinreceptor(TfR)forironacquisition.Botharetranscribedfromtheactivetelomericexpressionsite.VSGis a GPI2homodimer;TfRisa GPI1heterodimerof GPI-anchoredESAG6andESAG7.GPI-valencecorrelateswithsecretoryprogressionandfatein bloodstreamtrypanosomes:VSG(GPI2) is a surfacepro-tein;truncatedVSG(GPI0) is degradedin thelysosome;andnativeTfR(GPI1) localizesintheflagellarpocket.Tf:Festarvationresultsin up-regulationandredistributionof TfRto theplasmamembranesuggestinga saturablemechanismforflagellarpocketretention.How-ever,becausesuchsurfaceTfRis non-functionalforligandbindingweproposedthatit rep-resentsGPI2ESAG6homodimersthatareunableto bindtransferrin—therebymimickingnativeVSG.Wenowexploita novelRNAisystemforsimultaneouslethalsilencingof allnativeTfRsubunitsandexclusivein-situexpressionof RNAi-resistant TfRvariantswithvalencesof GPI0–2. Ourresultsconformto thevalencemodel:GPI0ESAG7homodimerstraffickto thelysosomeandGPI2ESAG6homodimersto thecellsurface.However,whenexpressedaloneESAG6is up-regulated~7-fold,leavingtheissueof saturableretentionintheflagellarpocketin question.Therefore,wecreatedanRNAi-resistant GPI2TfRheterodi-merbyfusingtheC-terminaldomainof ESAG6to ESAG7.Co-expressionwithESAG6gen-eratesa functionalheterodimericGPI2TfRthatrestoresTf uptakeandcellviability,andlocalizesto thecellsurface,withoutoverexpression.Theseresultsresolvethelongstandingissueof TfRtraffickingunderover-expressionandconfirmGPIvalenceasa criticaldetermi-nantof intracellularsortingin trypanosomes.
  • Journal article
    Westhorpe F, 2017,

    Postdocs, What Would You Tell Your Younger Self?

    , Cell, Vol: 168, Pages: 745-748, ISSN: 0092-8674
  • Journal article
    Tiengwe C, Muratore KA, Bangs JD, 2016,

    Surface proteins, ERAD and antigenic variation in Trypanosoma brucei

    , Cellular Microbiology, Vol: 18, Pages: 1673-1688, ISSN: 1462-5814

    Variant surface glycoprotein (VSG) is central to antigenic variation in African trypanosomes. Although much prior work documents that VSG is efficiently synthesized and exported to the cell surface, it was recently claimed that 2–3 fold more is synthesized than required, the excess being eliminated by ER‐Associated Degradation (ERAD) (Field et al., 2010). We now reinvestigate VSG turnover and find no evidence for rapid degradation, consistent with a model whereby VSG synthesis is precisely regulated to match requirements for a functional surface coat on each daughter cell. However, using a mutated version of the ESAG7 subunit of the transferrin receptor (E7:Ty) we confirm functional ERAD in trypanosomes. E7:Ty fails to assemble into transferrin receptors and accumulates in the ER, consistent with retention of misfolded protein, and its turnover is selectively rescued by the proteasomal inhibitor MG132. We also show that ER accumulation of E7:Ty does not induce an unfolded protein response. These data, along with the presence of ERAD orthologues in the Trypanosoma brucei genome, confirm ERAD in trypanosomes. We discuss scenarios in which ERAD could be critical to bloodstream parasites, and how these may have contributed to the evolution of antigenic variation in trypanosomes.
  • Journal article
    Marques CA, Tiengwe C, Lemgruber L, Damasceno JD, Scott A, Paape D, Marcello L, McCulloch Ret al., 2016,

    Diverged composition and regulation of the Trypanosoma brucei origin recognition complex that mediates DNA replication initiation

    , Nucleic Acids Research, Vol: 44, Pages: 4763-4784, ISSN: 0305-1048

    Initiation of DNA replication depends upon recog-nition of genomic sites, termed origins, by AAA+ATPases. In prokaryotes a single factor binds eachorigin, whereas in eukaryotes this role is playedby a six-protein origin recognition complex (ORC).Why eukaryotes evolved a multisubunit initiator, andthe roles of each component, remains unclear. InTrypanosoma brucei, an ancient unicellular eukary-ote, only one ORC-related initiator, TbORC1/CDC6,has been identified by sequence homology. Herewe show that three TbORC1/CDC6-interacting fac-tors also act inT. bruceinuclear DNA replicationand demonstrate that TbORC1/CDC6 interacts in ahigh molecular complex in which a diverged Orc4homologue and one replicative helicase subunit canalso be found. Analysing the subcellular localizationof four TbORC1/CDC6-interacting factors during thecell cycle reveals that one factor, TbORC1B, is nota static constituent of ORC but displays S-phaserestricted nuclear localization and expression, sug-gesting it positively regulates replication. This workshows that ORC architecture and regulation are di-verged features of DNA replication initiation inT. bru-cei, providing new insight into this key stage of eu-karyotic genome copying.
  • Journal article
    Tiengwe C, Brown AENA, Bangs JD, 2015,

    Unfolded Protein Response Pathways in Bloodstream-Form Trypanosoma brucei?

    , Eukaryot Cell, Vol: 14, Pages: 1094-1101

    The unfolded protein response (UPR) is a stress mechanism to cope with misfolded proteins in the early secretory pathway, the hallmark being transcriptional upregulation of endoplasmic reticulum (ER) molecular chaperones such as BiP and protein disulfide isomerase. Despite the lack of transcriptional regulation and the absence of the classical UPR machinery, African trypanosomes apparently respond to persistent ER stress by a UPR-like response, including upregulation of BiP, and a related spliced leader silencing (SLS) response whereby SL RNA transcription is shut down. Initially observed by knockdown of the secretory protein translocation machinery, both responses are also induced by chemical agents known to elicit UPR in mammalian cells (H. Goldshmidt, D. Matas, A. Kabi, A. Carmi, R. Hope, S. Michaeli, PLoS Pathog 6:e1000731, 2010, http://dx.doi.org/10.1371/journal.ppat.1000731). As these findings were generated primarily in procyclic-stage trypanosomes, we have investigated both responses in pathogenic bloodstream-stage parasites. RNA interference (RNAi) silencing of the core translocon subunit Trypanosoma brucei Sec61α (TbSec61α) failed to induce either response. Interestingly, cell growth halted within 16 h of silencing, but sufficient TbSec61α remained to allow full competence for translocation of nascent secretory proteins for up to 24 h, indicating that replication is finely coupled with the capacity to synthesize and transport secretory cargo. Tunicamycin and thapsigargin at concentrations compatible with short-term (4 h) and long-term (24 h) viability also failed to induce any of the indicators of UPR-like or SLS responses. Dithiothreitol (DTT) was lethal at all concentrations tested. These results indicate that UPR-like and SLS responses to persistent ER stress do not occur in bloodstream-stage trypanosomes.
  • Journal article
    Tiengwe C, Brown AENA, Bangs JD, 2015,

    Unfolded Protein Response Pathways in Bloodstream-Form <i>Trypanosoma brucei</i>?

    , EUKARYOTIC CELL, Vol: 14, Pages: 1094-1101, ISSN: 1535-9778
  • Journal article
    Kammers K, Cole RN, Tiengwe C, Ruczinski Iet al., 2015,

    Detecting significant changes in protein abundance

    , EuPA Open Proteomics, Vol: 7, Pages: 11-19, ISSN: 2212-9685

    We review and demonstrate how an empirical Bayes method, shrinking a protein's sample variance towards a pooled estimate, leads to far more powerful and stable inference to detect significant changes in protein abundance compared to ordinary t-tests. Using examples from isobaric mass labelled proteomic experiments we show how to analyze data from multiple experiments simultaneously, and discuss the effects of missing data on the inference. We also present easy to use open source software for normalization of mass spectrometry data and inference based on moderated test statistics.
  • Journal article
    Tiengwe C, Marques CA, McCulloch R, 2014,

    Nuclear DNA replication initiation in kinetoplastid parasites: new insights into an ancient process

    , TRENDS IN PARASITOLOGY, Vol: 30, Pages: 27-36, ISSN: 1471-4922
  • Journal article
    Povelones ML, Tiengwe C, Gluenz E, Gull K, Englund PT, Jensen REet al., 2013,

    Mitochondrial shape and function in trypanosomes requires the outer membrane protein, TbLOK1

    , Molecular Microbiology, Vol: 87, Pages: 713-729, ISSN: 0950-382X

    In an RNAi library screen for loss of kinetoplast DNA (kDNA), we identified an uncharacterized Trypanosoma brucei protein, named TbLOK1, required for maintenance of mitochondrial shape and function. We found the TbLOK1 protein located in discrete patches in the mitochondrial outer membrane. Knock‐down of TbLOK1 in procyclic trypanosomes caused the highly interconnected mitochondrial structure to collapse, forming an unbranched tubule remarkably similar to the streamlined organelle seen in the bloodstream form. Following RNAi, defects in mitochondrial respiration, inner membrane potential and mitochondrial transcription were observed. At later times following TbLOK1 depletion, kDNA was lost and a more drastic alteration in mitochondrial structure was found. Our results demonstrate the close relationship between organelle structure and function in trypanosomes.
  • Journal article
    Tiengwe C, Marcello L, Farr H, Dickens N, Kelly S, Swiderski M, Vaughan D, Gull K, Barry JD, Bell SD, McCulloch Ret al., 2012,

    Genome-wide Analysis Reveals Extensive Functional Interaction between DNA Replication Initiation and Transcription in the Genome of Trypanosoma brucei

    , Cell Reports, Vol: 2, Pages: 185-197, ISSN: 2211-1247

    Identification of replication initiation sites, termed origins, is a crucial step in understanding genome transmission in any organism. Transcription of the Trypanosoma brucei genome is highly unusual, with each chromosome comprising a few discrete transcription units. To understand how DNA replication occurs in the context of such organization, we have performed genome-wide mapping of the binding sites of the replication initiator ORC1/CDC6 and have identified replication origins, revealing that both localize to the boundaries of the transcription units. A remarkably small number of active origins is seen, whose spacing is greater than in any other eukaryote. We show that replication and transcription in T. brucei have a profound functional overlap, as reducing ORC1/CDC6 levels leads to genome-wide increases in mRNA levels arising from the boundaries of the transcription units. In addition, ORC1/CDC6 loss causes derepression of silent Variant Surface Glycoprotein genes, which are critical for host immune evasion.
  • Journal article
    Tiengwe C, Marcello L, Farr H, Gadelha C, Burchmore R, Barry JD, Bell SD, McCulloch Ret al., 2012,

    Identification of ORC1/CDC6-Interacting Factors in Trypanosoma brucei Reveals Critical Features of Origin Recognition Complex Architecture

    , PLoS ONE, Vol: 7, ISSN: 1932-6203

    DNA Replication initiates by formation of a pre-replication complex on sequences termed origins. In eukaryotes, the pre-replication complex is composed of the Origin Recognition Complex (ORC), Cdc6 and the MCM replicative helicase inconjunction with Cdt1. Eukaryotic ORC is considered to be composed of six subunits, named Orc1–6, and monomeric Cdc6is closely related in sequence to Orc1. However, ORC has been little explored in protists, and only a single ORC protein,related to both Orc1 and Cdc6, has been shown to act in DNA replication inTrypanosoma brucei. Here we identify threehighly diverged putativeT. bruceiORC components that interact with ORC1/CDC6 and contribute to cell division. Two ofthese factors are so diverged that we cannot determine if they are eukaryotic ORC subunit orthologues, or are parasite-specific replication factors. The other we show to be a highly diverged Orc4 orthologue, demonstrating that this is one ofthe most widely conserved ORC subunits in protists and revealing it to be a key element of eukaryotic ORC architecture.Additionally, we have examined interactions amongst theT. bruceiMCM subunits and show that this has the conventionaleukaryotic heterohexameric structure, suggesting that divergence in theT. bruceireplication machinery is limited to theearliest steps in origin licensing.

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Dr. Calvin Tiengwe
Dept. of Life Sciences,
503 Sir Ernst Chain Building,
Imperial College London,
SW7 2AZ, UK

c.tiengwe@imperial.ac.uk 

Funding