Larry Simpson, Ph.D.

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UCLA Professor, Microbiology, Immunology & Molecular Genetics

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Los Angeles, CA 90095
6-780 MRL
CAMPUS - 166222
Los Angeles, CA 90095

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Molecular biology of parasitic protozoa I am interested in the molecular biology of parasitic protozoa known as trypanosomes or kinetoplastid protozoa. In particular, we are investigating a novel type of RNA modification phenomenon termed ?RNA editing?, that occurs in the single mitochondrion. mRNA transcripts of the mitochondrial maxicircle DNA molecules are modified after transcription by the insertion and deletion of uridine residues at precise sites within coding regions to form a translatable sequence. The information for this editing is contained in small ?guide RNAs?, which hybridize to the pre-edited mRNA and somehow mediate the transfer of uridines to the editing sites. The guide RNAs are encoded mainly in the thousands of minicircular molecules linked by catenation in the single giant network of DNA present in the single mitochondrion of these cells. In some cases multiple overlapping gRNAs mediate the addition of hundreds of uridines at hundreds of sites. We are studying the mechanism of this unusual process by establishing an in vitro editing system. Several classes of ribonucleoprotein complexes appear to be involved, and these are being dissected and analyzed. Proteins involved in the editing process are being isolated and the genes cloned. In addition, we are interested in the evolution of RNA editing in these ancient lower eukaryotic cells. To this end we are analyzing editing in a variety of kinetoplastid protozoa, whose phylogenetic relationships we have determined. By a comparative analysis we can make some deductions about the evolution of this phenomenon. We are also studying the changes in the editing system that occur during prolonged culture of trypanosomes, which appear to involve the loss of minicircle sequence classes encoding specific guide RNA families. I am also interested in other aspects of the mitochondrial genetic system and mitochondrial biogenesis. Since there are no transfer RNAs encoded in the mitochondrial genome of trypanosomes, all the mt tRNAs must be imported, and the mechanism of this process is being actively studied in my laboratory. Mitochondrial transcription and translation are other processes in which I have a great interest.


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Eckers Elisabeth, Cyrklaff Marek, Simpson Larry, Deponte Marcel   Mitochondrial protein import pathways are functionally conserved among eukaryotes despite compositional diversity of the import machineries Biological chemistry, 2012; 393(6): 513-24.
Simpson Larry   A personal scientific odyssey Protist, 2011; 162(1): 188-206.
Li Feng, Herrera Jeremy, Zhou Sharleen, Maslov Dmitri A, Simpson Larry   Trypanosome REH1 is an RNA helicase involved with the 3'-5' polarity of multiple gRNA-guided uridine insertion/deletion RNA editing Proceedings of the National Academy of Sciences of the United States of America, 2011; 108(9): 3542-7.
Simpson Larry, Aphasizhev Ruslan, Lukes Julius, Cruz-Reyes Jorge   Guide to the nomenclature of kinetoplastid RNA editing: a proposal Protist, 2010; 161(1): 2-6.
Gao Guanghan, Rogers Kestrel, Li Feng, Guo Qiang, Osato Daren, Zhou Sharleen X, Falick Arnold M, Simpson Larry   Uridine insertion/deletion RNA editing in Trypanosomatids: specific stimulation in vitro of Leishmania tarentolae REL1 RNA ligase activity by the MP63 zinc finger protein Protist, 2010; 161(3): 489-96.
Simpson Larry   Musings on the real problems Protist, 2009; 160(1): 3.
Nebohácová Martina, Kim Christine E, Simpson Larry, Maslov Dmitri A   RNA editing and mitochondrial activity in promastigotes and amastigotes of Leishmania donovani International journal for parasitology, 2009; 39(6): 635-44.
Simpson Larry   Science is a hard mistress Protist, 2009; 160(4): 481-2.
Sharma Manjuli R, Booth Timothy M, Simpson Larry, Maslov Dmitri A, Agrawal Rajendra K   Structure of a mitochondrial ribosome with minimal RNA Proceedings of the National Academy of Sciences of the United States of America, 2009; 106(24): 9637-42.
Li Feng, Ge Peng, Hui Wong H, Atanasov Ivo, Rogers Kestrel, Guo Qiang, Osato Daren, Falick Arnold M, Zhou Z Hong, Simpson Larry   Structure of the core editing complex (L-complex) involved in uridine insertion/deletion RNA editing in trypanosomatid mitochondria Proceedings of the National Academy of Sciences of the United States of America, 2009; 106(30): 12306-10.
Osato Daren, Rogers Kestrel, Guo Qiang, Li Feng, Richmond Greg, Klug Felix, Simpson Larry   Uridine insertion/deletion RNA editing in trypanosomatid mitochondria: In search of the editosome RNA (New York, N.Y.), 2009; 15(7): 1338-44.
Jensen Robert E, Simpson Larry, Englund Paul T   What happens when Trypanosoma brucei leaves Africa Trends in parasitology, 2008; 24(10): 428-31.
Maslov Dmitri A, Spremulli Linda L, Sharma Manjuli R, Bhargava Kalpana, Grasso Domenick, Falick Arnold M, Agrawal Rajendra K, Parker Carol E, Simpson Larry   Proteomics and electron microscopic characterization of the unusual mitochondrial ribosome-related 45S complex in Leishmania tarentolae Molecular and biochemical parasitology, 2007; 152(2): 203-12.
Maslov Dmitri A, Simpson Larry   Strategies of kinetoplastid cryptogene discovery and analysis Methods in enzymology, 2007; 424(2): 127-39.
Rogers Kestrel, Gao Guanghan, Simpson Larry   Uridylate-specific 3' 5'-exoribonucleases involved in uridylate-deletion RNA editing in trypanosomatid mitochondria The Journal of biological chemistry, 2007; 282(40): 29073-80.
Simpson Larry   Death of the "ologies" Protist, 2006; 157(4): 361-2.
Maslov Dmitri A, Sharma Manjuli R, Butler Evelin, Falick Arnold M, Gingery Mari, Agrawal Rajendra K, Spremulli Linda L, Simpson Larry   Isolation and characterization of mitochondrial ribosomes and ribosomal subunits from Leishmania tarentolae Molecular and biochemical parasitology, 2006; 148(1): 69-78.
Kang Xuedong, Gao Guanghan, Rogers Kestrel, Falick Arnold M, Zhou Sharleen, Simpson Larry   Reconstitution of full-round uridine-deletion RNA editing with three recombinant proteins Proceedings of the National Academy of Sciences of the United States of America, 2006; 103(38): 13944-9.
Gao Guanghan, Simpson Agda M, Kang Xuedong, Rogers Kestrel, Nebohacova Martina, Li Feng, Simpson Larry   Functional complementation of Trypanosoma brucei RNA in vitro editing with recombinant RNA ligase Proceedings of the National Academy of Sciences of the United States of America, 2005; 102(13): 4712-7.
Trager Lillian, Spielman Andrew, Simpson Larry   Malaria, not down and certainly not out The American journal of tropical medicine and hygiene, 2005; 73(5): 824-5.
Kang Xuedong, Rogers Kestrel, Gao Guanghan, Falick Arnold M, Zhou Sharleen, Simpson Larry   Reconstitution of uridine-deletion precleaved RNA editing with two recombinant enzymes Proceedings of the National Academy of Sciences of the United States of America, 2005; 102(4): 1017-22.
Kang Xuedong, Falick Arnold M, Nelson Robert E, Gao Guanghan, Rogers Kestrel, Aphasizhev Ruslan, Simpson Larry   Disruption of the zinc finger motifs in the Leishmania tarentolae LC-4 (=TbMP63) L-complex editing protein affects the stability of the L-complex The Journal of biological chemistry, 2004; 279(6): 3893-9.
Simpson Larry, Aphasizhev Ruslan, Gao Guanghan, Kang Xuedong   Mitochondrial proteins and complexes in Leishmania and Trypanosoma involved in U-insertion/deletion RNA editing RNA (New York, N.Y.), 2004; 10(2): 159-70.
Aphasizhev Ruslan, Aphasizheva Inna, Simpson Larry   Multiple terminal uridylyltransferases of trypanosomes FEBS letters, 2004; 572(1-3): 15-8.
Aphasizheva Inna, Aphasizhev Ruslan, Simpson Larry   RNA-editing terminal uridylyl transferase 1: identification of functional domains by mutational analysis The Journal of biological chemistry, 2004; 279(23): 24123-30.
Nelson Robert E, Aphasizheva Inna, Falick Arnold M, Nebohacova Martina, Simpson Larry   The I-complex in Leishmania tarentolae is an uniquely-structured F(1)-ATPase Molecular and biochemical parasitology, 2004; 135(2): 221-4.
Aphasizhev Ruslan, Aphasizheva Inna, Nelson Robert E, Simpson Larry   A 100-kD complex of two RNA-binding proteins from mitochondria of Leishmania tarentolae catalyzes RNA annealing and interacts with several RNA editing components RNA (New York, N.Y.), 2003; 9(1): 62-76.
Aphasizhev Ruslan, Aphasizheva Inna, Simpson Larry   A tale of two TUTases Proceedings of the National Academy of Sciences of the United States of America, 2003; 100(19): 10617-22.
Hong Min, Simpson Larry   Genomic organization of Trypanosoma brucei kinetoplast DNA minicircles Protist, 2003; 154(2): 265-79.
Gao Guanghan, Simpson Larry   Is the Trypanosoma brucei REL1 RNA ligase specific for U-deletion RNA editing, and is the REL2 RNA ligase specific for U-insertion editing? The Journal of biological chemistry, 2003; 278(30): 27570-4.
Aphasizhev Ruslan, Aphasizheva Inna, Nelson Robert E, Gao Guanghan, Simpson Agda M, Kang Xuedong, Falick Arnold M, Sbicego Sandro, Simpson Larry   Isolation of a U-insertion/deletion editing complex from Leishmania tarentolae mitochondria The EMBO journal, 2003; 22(4): 913-24.
Sbicego Sandro, Alfonzo Juan D, Estévez Antonio M, Rubio Mary Anne T, Kang Xuedong, Turck Christoph W, Peris Marian, Simpson Larry   RBP38, a novel RNA-binding protein from trypanosomatid mitochondria, modulates RNA stability Eukaryotic cell, 2003; 2(3): 560-8.
Simpson Larry, Sbicego Sandro, Aphasizhev Ruslan   Uridine insertion/deletion RNA editing in trypanosome mitochondria: a complex business RNA (New York, N.Y.), 2003; 9(3): 265-76.
Kaneko Tomonori, Suzuki Takeo, Kapushoc Stephen T, Rubio Mary Anne, Ghazvini Jafar, Watanabe Kimitsuna, Simpson Larry, Suzuki Tsutomu   Wobble modification differences and subcellular localization of tRNAs in Leishmania tarentolae: implication for tRNA sorting mechanism The EMBO journal, 2003; 22(3): 657-67.
Monzani Paulo S, Alfonzo Juan D, Simpson Larry, Oliva Glaucius, Thiemann Otavio H   Cloning, characterization and preliminary crystallographic analysis of Leishmania hypoxanthine-guanine phosphoribosyltransferase Biochimica et biophysica acta, 2002; 1598(1-2): 3-9.
Kapushoc Stephen T, Alfonzo Juan D, Simpson Larry   Differential localization of nuclear-encoded tRNAs between the cytosol and mitochondrion in Leishmania tarentolae RNA (New York, N.Y.), 2002; 8(1): 57-68.
Simpson Larry   Malaria--the biological terminator Protist, 2002; 153(1): 7-8.
Crain Pamela F, Alfonzo Juan D, Rozenski Jef, Kapushoc Stephen T, McCloskey James A, Simpson Larry   Modification of the universally unmodified uridine-33 in a mitochondria-imported edited tRNA and the role of the anticodon arm structure on editing efficiency RNA (New York, N.Y.), 2002; 8(6): 752-61.
Aphasizhev Ruslan, Sbicego Sandro, Peris Marian, Jang Sei-Heon, Aphasizheva Inna, Simpson Agda M, Rivlin Anatoly, Simpson Larry   Trypanosome mitochondrial 3' terminal uridylyl transferase (TUTase): the key enzyme in U-insertion/deletion RNA editing Cell, 2002; 108(5): 637-48.
Aphasizhev, R Simpson, L   Isolation and characterization of a U-specific 3'-5'-exonuclease from mitochondria of Leishmania tarentolae The Journal of biological chemistry. , 2001; 276(24): 21280-4.
Carillo, R., Thiemann, O.H., Alfonzo, J.D., Simpson, L.   Uridine insertion/deletion RNA editing in Leishmania tarentolae mitochondria shows cell cycle dependence, Mol. Biochem. Parasitol, 2001; 113 : 175-181 .
Kapushoc, ST Alfonzo, JD Rubio, MA Simpson, L   End processing precedes mitochondrial importation and editing of tRNAs in Leishmania tarentolae The Journal of biological chemistry. , 2000; 275(48): 37907-14.
Simpson, L Thiemann, OH Savill, NJ Alfonzo, JD Maslov, DA   Evolution of RNA editing in trypanosome mitochondria Proceedings of the National Academy of Sciences of the United States of America. , 2000; 97(13): 6986-93.
Rubio, MA Liu, X Yuzawa, H Alfonzo, JD Simpson, L   Selective importation of RNA into isolated mitochondria from Leishmania tarentolae RNA (New York, N.Y.) , 2000; 6(7): 988-1003.
Alfonzo, J.D., Blanc, V., Estevez, A.M., Rubio, M.A.T., Simpson, L.   C to U editing of anticodon of imported mitochondrial tRNATrp allows decoding of UGA stop codon in Leishmania, EMBO J, 1999; 18: 7056-7062.
Kapushoc, ST Simpson, L   In vitro uridine insertion RNA editing mediated by cis-acting guide RNAs RNA (New York, N.Y.) , 1999; 5(5): 656-69.
Estevez, A.M., Kierzenbaum, F., Wirtz, E., Bringaud, F., Grunstein, J., Simpson, L.   Knockoutof the glutamate dehydrogenase gene in bloodstream Trypanosoma brucei in culture has no effect on editing of mitochondrial mRNAs, Mol. Biochem. Parasitol, 1999; 100: 5-17.
Estevez,A.E., Thiemann, O.H., Alfonzo, J.D., Simpson, L.   T7 RNA polymerase driven transcription in mitochondria of Leishmania tarentolae and Trypanosoma brucei, Mol. Biochem. Parasitol, 1999; 103: 251-259.
Blanc, V., Alfonzo, J.D., Aphasizhev, R., Simpson, L.   The mitochondrial RNA ligase from Leishmania tarentolae can join RNA molecules bridged by a complementary RNA, J. Biol. Chem. , 1999; 274: 24289-24296.
Estevez, A.M., Simpson, L.   Uridine insertion/deletion RNA editing in trypanosome mitochondria - a review, Gene, 1999; 240: 247-260.
Alfonzo, JD Thiemann, OH Simpson, L   Purification and characterization of MAR1. A mitochondrial associated ribonuclease from Leishmania tarentolae The Journal of biological chemistry. , 1998; 273(45): 30003-11.
Alfonzo, JD Thiemann, O Simpson, L   The mechanism of U insertion/deletion RNA editing in kinetoplastid mitochondria Nucleic acids research. , 1997; 25(19): 3751-9.
Byrne, EM Connell, GJ Simpson, L   Guide RNA-directed uridine insertion RNA editing in vitro The EMBO journal. , 1996; 15(23): 6758-65.

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Adenosine Triphosphate Amino Acid Motifs Amino Acid Sequence Aminohydrolases Animal Diseases Animals Antibodies Anticodon Antigenic Variation Antiprotozoal Agents Back Baculoviridae Base Pairing Base Sequence Biological Phenomena Biological Transport Biology Brain Carbon-Oxygen Ligases Catalysis Cell Cycle Cell Differentiation Cell Nucleus Cells Chagas Disease Chromatography, Ion Exchange Cloning, Molecular Conserved Sequence Cryoelectron Microscopy Cytidine DNA DNA Primers DNA Replication DNA, Kinetoplast DNA, Protozoan Disease Down-Regulation Electron Transport Complex IV Electrophoresis, Gel, Two-Dimensional Electrophoresis, Polyacrylamide Gel Escherichia coli Exonucleases Gas Chromatography-Mass Spectrometry Gene Deletion Gene Expression Regulation Gene Targeting Genes, Protozoan Genetic Vectors Genome Genome, Protozoan Goals Gold History, 20th Century History, 21st Century Holoenzymes Humans Hydrolysis Immunoprecipitation Insect Vectors Kinetics Kinetoplastida Knowledge Laboratories Leishmania Leishmania major Leishmaniasis Life Cycle Stages Ligation Lizards Macromolecular Substances Magnesium Malaria Mass Spectrometry Methylation Mitochondria Mitochondrial Proteins Models, Biological Molecular Biology Molecular Sequence Data Molecular Structure Molecular Weight Multiprotein Complexes Mutagenesis, Site-Directed Mutation Nature Nucleic Acid Conformation Nucleic Acid Probes Nucleotides Oxygen Consumption Parasites Plasmodium Protein Binding Protein Structure, Quaternary Protein Structure, Secondary Protein Structure, Tertiary Protein Subunits Protein Transport Proteins Protozoan Proteins RNA RNA Editing RNA Helicases RNA Interference RNA Ligase (ATP) RNA Nucleotidyltransferases RNA Processing, Post-Transcriptional RNA, Double-Stranded RNA, Guide RNA, Messenger RNA, Protozoan RNA, Transfer RNA-Binding Proteins Recombinant Proteins Research Reverse Transcriptase Polymerase Chain Reaction Ribonucleoproteins Ribosomal Proteins Ribosomes Sequence Alignment Sequence Analysis, DNA Sequence Homology, Amino Acid Spectrometry, Fluorescence Spectrometry, Gamma Spectrometry, Mass, Electrospray Ionization Spectrometry, Mass, Fast Atom Bombardment Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization Spectrometry, Mass, Secondary Ion Spectrometry, X-Ray Emission Subcellular Fractions Substrate Specificity Systems Analysis Tandem Mass Spectrometry Terminology as Topic Time Time Factors Trans-Splicing Transcription, Genetic Transfection Transfer RNA Aminoacylation Translations Trypanosoma Trypanosoma brucei brucei Uracil Uridine Uridine Triphosphate Zinc Fingers

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