scholarly journals In Trypanosoma brucei RNA Editing, Band II Enables Recognition Specifically at Each Step of the U Insertion Cycle

2005 ◽  
Vol 25 (7) ◽  
pp. 2785-2794 ◽  
Author(s):  
Julie A. Law ◽  
Catherine E. Huang ◽  
Sean F. O'Hearn ◽  
Barbara Sollner-Webb
Keyword(s):  
Rna Interference ◽  
Trypanosoma Brucei ◽  
Rna Editing ◽  
Cell Lines ◽  
Protein Recognition ◽  
Essential Nature ◽  
Insertion And Deletion ◽  
Insertion Sites

ABSTRACT Trypanosome RNA editing is the posttranscriptional insertion and deletion of uridylate (U) residues, often to a massive extent, through cycles of cleavage, U addition or U removal, and ligation. These editing cycles are catalyzed by a complex that we purified to seven major proteins (bands I through VII). Here we analyze the role of band II using extracts of clonal band II RNA interference (RNAi) cell lines prepared by a rapid protocol that enables retention of activities that are lost during traditional extract preparation. By individually scoring each step of editing, we show that band II is critical for all steps of U insertion but is not important for any of the steps of U deletion or for their coordination into the U deletion cycle. This specificity supports the long- standing model that U-insertional and U-deletional activities are separated within the editing complex. Furthermore, by assaying the basic activities of the enzymes that catalyze the steps of U insertion, independent of their action in editing, we show that band II is not any of those enzymes. Rather, band II enables endonuclease action at authentic U insertion sites, terminal-uridylyl-transferase (TUTase) action at cleaved U insertion sites, and U-insertion-specific ligase (band V/IREL) action in the editing complex. Thus, band II facilitates each step of U insertion by providing proper RNA and/or protein recognition. We propose that band II (TbMP81) be called IRER, indicating its essential nature in U-insertional RNA editing recognition.

scholarly journals In Trypanosoma brucei RNA Editing, TbMP18 (Band VII) Is Critical for Editosome Integrity and for both Insertional and Deletional Cleavages

2006 ◽  
Vol 27 (2) ◽  
pp. 777-787 ◽  
Author(s):  
Julie A. Law ◽  
Sean O'Hearn ◽  
Barbara Sollner-Webb
Keyword(s):  
Rna Interference ◽  
Trypanosoma Brucei ◽  
Rna Editing ◽  
Protein Complex ◽  
Substrate Recognition ◽  
The Other ◽  
Major Protein

ABSTRACT In trypanosome RNA editing, uridylate (U) residues are inserted and deleted at numerous sites within mitochondrial pre-mRNAs by an ∼20S protein complex that catalyzes cycles of cleavage, U addition/U removal, and ligation. We used RNA interference to deplete TbMP18 (band VII), the last unexamined major protein of our purified editing complex, showing it is essential. TbMP18 is critical for the U-deletional and U-insertional cleavages and for integrity of the ∼20S editing complex, whose other major components, TbMP99, TbMP81, TbMP63, TbMP52, TbMP48, TbMP42 (bands I through VI), and TbMP57, instead sediment as ∼10S associations. Additionally, TbMP18 augments editing substrate recognition by the TbMP57 terminal U transferase, possibly aiding the recognition component, TbMP81. The other editing activities and their coordination in precleaved editing remain active in the absence of TbMP18. These data are reminiscent of the data on editing subcomplexes reported by A. Schnaufer et al. (Mol. Cell 12:307-319, 2003) and suggest that these subcomplexes are held together in the ∼20S complex by TbMP18, as was proposed previously. Our data additionally imply that the proteins are less long-lived in these subcomplexes than they are when held in the complete editing complex. The editing endonucleolytic cleavages being lost when the editing complex becomes fragmented, as upon TbMP18 depletion, should be advantageous to the trypanosome, minimizing broken mRNAs.

scholarly journals TbMP44 Is Essential for RNA Editing and Structural Integrity of the Editosome in Trypanosoma brucei

2003 ◽  
Vol 2 (3) ◽  
pp. 578-587 ◽  
Author(s):  
Bingbing Wang ◽  
Nancy Lewis Ernst ◽  
Setareh S. Palazzo ◽  
Aswini K. Panigrahi ◽  
Reza Salavati ◽  
...  
Keyword(s):  
Gene Expression ◽  
Cell Growth ◽  
Trypanosoma Brucei ◽  
Rna Editing ◽  
Structural Integrity ◽  
Sedimentation Coefficient ◽  
Sequence Database ◽  
Multiprotein Complex ◽  
Database Analysis ◽  
Insertion And Deletion

ABSTRACT RNA editing produces mature mitochondrial mRNAs in trypanosomatids by the insertion and deletion of uridylates. It is catalyzed by a multiprotein complex, the editosome. We identified TbMP44 among the components of enriched editosomes by a combination of mass spectrometry and DNA sequence database analysis. Inactivation of an ectopic TbMP44 allele in cells in which the endogenous alleles were disrupted abolished RNA editing, inhibited cell growth, and was eventually lethal to bloodstream form trypanosomes. Loss of TbMP44 mRNA was followed initially by a reduction in the editosome sedimentation coefficient and then by the absence of other editosome proteins despite the presence of the mRNA. Reactivation of TbMP44 gene expression resulted in the resumption of cell growth and the reappearance of editosomes. These data indicate that TbMP44 is a component of the editosome that is essential for editing and critical for the structural integrity of the editosome.

scholarly journals The Two RNA Ligases of the Trypanosoma brucei RNA Editing Complex: Cloning the Essential Band IV Gene and Identifying the Band V Gene

2001 ◽  
Vol 21 (4) ◽  
pp. 979-989 ◽  
Author(s):  
Laura N. Rusché ◽  
Catherine E. Huang ◽  
Kenneth J. Piller ◽  
Michael Hemann ◽  
Elizabeth Wirtz ◽  
...  
Keyword(s):  
Trypanosoma Brucei ◽  
Rna Editing ◽  
Mrna Levels ◽  
Mitochondrial Targeting ◽  
Terminal Sequence ◽  
Partial Amino Acid Sequence ◽  
Rna Ligase ◽  
E Coli ◽  
Insertion And Deletion ◽  
Mitochondrial Transcripts

ABSTRACT Kinetoplastid RNA editing is a posttranscriptional insertion and deletion of U residues in mitochondrial transcripts that involves RNA ligase. A complex of seven different polypeptides purified fromTrypanosoma brucei mitochondria that catalyzes accurate RNA editing contains RNA ligases of ∼57 kDa (band IV) and ∼50 kDa (band V). From a partial amino acid sequence, cDNA and genomic clones of band IV were isolated, making it the first cloned component of the minimal RNA editing complex. It is indeed an RNA ligase, for when expressed inEscherichia coli, the protein autoadenylylates and catalyzes RNA joining. Overexpression studies revealed that T. brucei can regulate of total band IV protein at the level of translation or protein stability, even upon massively increased mRNA levels. The protein's mitochondrial targeting was confirmed by its location, size when expressed in T. brucei and E. coli, and N-terminal sequence. Importantly, genetic knockout studies demonstrated that the gene for band IV is essential in procyclic trypanosomes. The band IV and band V RNA ligases of the RNA editing complex therefore serve different functions. We also identified the gene for band V RNA ligase, a protein much more homologous to band IV than to other known ligases.

scholarly journals Role of p38 in Replication of Trypanosoma brucei Kinetoplast DNA

2006 ◽  
Vol 26 (14) ◽  
pp. 5382-5393 ◽  
Author(s):  
Beiyu Liu ◽  
Henrik Molina ◽  
Dario Kalume ◽  
Akhilesh Pandey ◽  
Jack D. Griffith ◽  
...  
Keyword(s):  
Rna Interference ◽  
Dna Replication ◽  
Mitochondrial Genome ◽  
Dna Synthesis ◽  
Trypanosoma Brucei ◽  
Replication Origin ◽  
Mitochondrial Protein ◽  
Kinetoplast Dna ◽  
Z Dna

ABSTRACT Trypanosomes have an unusual mitochondrial genome, called kinetoplast DNA, that is a giant network containing thousands of interlocked minicircles. During kinetoplast DNA synthesis, minicircles are released from the network for replication as θ-structures, and then the free minicircle progeny reattach to the network. We report that a mitochondrial protein, which we term p38, functions in kinetoplast DNA replication. RNA interference (RNAi) of p38 resulted in loss of kinetoplast DNA and accumulation of a novel free minicircle species named fraction S. Fraction S minicircles are so underwound that on isolation they become highly negatively supertwisted and develop a region of Z-DNA. p38 binds to minicircle sequences within the replication origin. We conclude that cells with RNAi-induced loss of p38 cannot initiate minicircle replication, although they can extensively unwind free minicircles.

scholarly journals Role of a 300-Kilodalton Nuclear Complex in the Maturation of Trypanosoma brucei Initiator Methionyl-tRNA

2004 ◽  
Vol 3 (4) ◽  
pp. 893-899 ◽  
Author(s):  
George K. Arhin ◽  
Shuiyuan Shen ◽  
Henriette Irmer ◽  
Elisabetta Ullu ◽  
Christian Tschudi
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Rna Interference ◽  
Trypanosoma Brucei ◽  
Unicellular Eukaryote ◽  
Down Regulation ◽  
Parasitic Protozoa ◽  
Initiator Trna ◽  
Nuclear Complex ◽  
Posttranscriptional Processing

ABSTRACT tRNAs are transcribed as precursors containing 5′ leader and 3′ extensions that are removed by a series of posttranscriptional processing reactions to yield functional mature tRNAs. Here, we examined the maturation pathway of tRNAMet in Trypanosoma brucei, an early divergent unicellular eukaryote. We identified an approximately 300-kDa complex located in the nucleus of T. brucei that is required for trimming the 5′ leader of initiator tRNAMet precursors. One of the subunits of the complex (T. brucei MT40 [TbMT40]) is a putative methyltransferase and a homolog of Saccharomyces cerevisiae Gcd14, which is essential for 1-methyladenosine modification in tRNAs. Down-regulation of TbMT40 by RNA interference resulted in the accumulation of precursor initiator tRNAMet containing 5′ extensions but processed 3′ ends. In addition, immunoprecipitations with anti-La antibodies revealed initiator tRNAMet molecules with 5′ and 3′ extensions in TbMT40-silenced cells, albeit at a much lower level. Interestingly, silencing of TbMT40, as well as of TbMT53, a second subunit of the complex, led to an increase in the levels of mature elongator tRNAMet. Taken together, our data provide a glance at the maturation of tRNAs in parasitic protozoa and suggest that at least for initiator tRNAMet, 3′ trimming precedes 5′ processing.

scholarly journals RNA Editing in Trypanosoma brucei Requires Three Different Editosomes

2007 ◽  
Vol 28 (1) ◽  
pp. 122-130 ◽  
Author(s):  
Jason Carnes ◽  
James Raffaello Trotter ◽  
Adam Peltan ◽  
Michele Fleck ◽  
Kenneth Stuart
Keyword(s):  
Trypanosoma Brucei ◽  
Rna Editing ◽  
Editing Site ◽  
Unexpected Finding ◽  
Rnase Iii ◽  
Growth And Survival ◽  
Insertion And Deletion ◽  
Additional Level

ABSTRACT Trypanosoma brucei has three distinct ∼20S editosomes that catalyze RNA editing by the insertion and deletion of uridylates. Editosomes with the KREN1 or KREN2 RNase III type endonucleases specifically cleave deletion and insertion editing site substrates, respectively. We report here that editosomes with KREPB2, which also has an RNase III motif, specifically cleave cytochrome oxidase II (COII) pre-mRNA insertion editing site substrates in vitro. Conditional repression and mutation studies also show that KREPB2 is an editing endonuclease specifically required for COII mRNA editing in vivo. Furthermore, KREPB2 expression is essential for the growth and survival of bloodstream forms. Thus, editing in T. brucei requires at least three compositionally and functionally distinct ∼20S editosomes, two of which distinguish between different insertion editing sites. This unexpected finding reveals an additional level of complexity in the RNA editing process and suggests a mechanism for how the selection of sites for editing in vivo is controlled.

scholarly journals Dyskinetoplastic Trypanosoma brucei Contains Functional Editing Complexes

2003 ◽  
Vol 2 (3) ◽  
pp. 569-577 ◽  
Author(s):  
Gonzalo J. Domingo ◽  
Setareh S. Palazzo ◽  
Bingbing Wang ◽  
Brian Pannicucci ◽  
Reza Salavati ◽  
...  
Keyword(s):  
Trypanosoma Brucei ◽  
Rna Editing ◽  
Trypanosoma Evansi ◽  
Wild Type ◽  
Single Class ◽  
Catalytic Activities ◽  
Guide Rnas ◽  
Insertion And Deletion ◽  
And Function

ABSTRACT Mitochondrial pre-mRNAs undergo posttranscriptional RNA editing as directed by small guide RNAs (gRNAs) to produce functional mRNAs in kinetoplastid protozoa. The pre-mRNAs and gRNAs are encoded in the maxicircle and minicircle components, respectively, of the kinetoplastid mitochondrial DNA (kDNA), and editing is catalyzed by a multienzyme protein complex. Trypanosoma evansi AnTat3/3, which lacks maxicircles but retains a single class of minicircles, and a dyskinetoplastic mutant of Trypanosoma brucei EATRO164, which is devoid of kDNA, were both shown to retain genes and proteins for the editing complex. The proteins are present in complexes that immunoprecipitate and sediment indistinguishably from wild-type complexes. The complexes catalyze precleaved insertion and deletion editing as well as full-round deletion editing in vitro. Thus, mutants which lack the natural substrates for RNA editing and all or most gRNAs retain editing complexes that contain the four primary catalytic activities of editing and function in editing, at least in vitro. Therefore neither pre-mRNA nor gRNA is required to form functional RNA-editing complexes.

scholarly journals Separate Insertion and Deletion Subcomplexes of the Trypanosoma brucei RNA Editing Complex

2003 ◽  
Vol 12 (2) ◽  
pp. 307-319 ◽  
Author(s):  
Achim Schnaufer ◽  
Nancy Lewis Ernst ◽  
Setareh S Palazzo ◽  
Jeff O'Rear ◽  
Reza Salavati ◽  
...  
Keyword(s):  
Trypanosoma Brucei ◽  
Rna Editing ◽  
Insertion And Deletion

scholarly journals The Centriole Cartwheel Protein SAS-6 in Trypanosoma brucei Is Required for Probasal Body Biogenesis and Flagellum Assembly

2015 ◽  
Vol 14 (9) ◽  
pp. 898-907 ◽  
Author(s):  
Huiqing Hu ◽  
Yi Liu ◽  
Qing Zhou ◽  
Sara Siegel ◽  
Ziyin Li
Keyword(s):  
Cell Cycle ◽  
Rna Interference ◽  
Trypanosoma Brucei ◽  
Basal Body ◽  
Essential Role ◽  
Microtubule Organizing Center ◽  
Content Type ◽  
Evolutionarily Conserved ◽  
Organizing Center

ABSTRACT The centriole in eukaryotes functions as the cell's microtubule-organizing center (MTOC) to nucleate spindle assembly, and its biogenesis requires an evolutionarily conserved protein, SAS-6, which assembles the centriole cartwheel. Trypanosoma brucei , an early branching protozoan, possesses the basal body as its MTOC to nucleate flagellum biogenesis. However, little is known about the components of the basal body and their roles in basal body biogenesis and flagellum assembly. Here, we report that the T. brucei SAS-6 homolog, TbSAS-6, is localized to the mature basal body and the probasal body throughout the cell cycle. RNA interference (RNAi) of TbSAS-6 inhibited probasal body biogenesis, compromised flagellum assembly, and caused cytokinesis arrest. Surprisingly, overexpression of TbSAS-6 in T. brucei also impaired probasal body duplication and flagellum assembly, contrary to SAS-6 overexpression in humans, which produces supernumerary centrioles. Furthermore, we showed that depletion of T. brucei Polo-like kinase, TbPLK, or inhibition of TbPLK activity did not abolish TbSAS-6 localization to the basal body, in contrast to the essential role of Polo-like kinase in recruiting SAS-6 to centrioles in animals. Altogether, these results identified the essential role of TbSAS-6 in probasal body biogenesis and flagellum assembly and suggest the presence of a TbPLK-independent pathway governing basal body duplication in T. brucei .

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