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See detailThe ARG9 Gene Encodes the Plastid-Resident N-Acetyl Ornithine Aminotransferase in the Green Alga Chlamydomonas reinhardtii
Remacle, Claire ULg; Cline, Sara; Boutaffala, Layla ULg et al

in Eukaryotic Cell (2009), 8(9), 1460-1463

Here we report the characterization of the Chlamydomonas reinhardtii gene ARG9, encoding the plastid resident N-acetyl ornithine aminotransferase, which is involved in arginine synthesis. Integration of ... [more ▼]

Here we report the characterization of the Chlamydomonas reinhardtii gene ARG9, encoding the plastid resident N-acetyl ornithine aminotransferase, which is involved in arginine synthesis. Integration of an engineered ARG9 cassette in the plastid chromosome of the nuclear arg9 mutant restores arginine prototrophy. This suggests that ARG9 could be used as a new selectable marker for plastid transformation. [less ▲]

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See detailND3 and ND4L subunits of mitochondrial complex I, both nucleus encoded in Chlamydomonas reinhardtii, are required for activity and assembly of the enzyme
Cardol, Pierre ULg; Lapaille, Marie ULg; Minet, P. et al

in Eukaryotic Cell (2006), 5(9), 1460-1467

Made of more than 40 subunits, the rotenone-sensitive NADH:ubiquinone oxidoreductase (complex I) is the most intricate membrane-bound enzyme of the mitochondrial respiratory chain. In vascular plants ... [more ▼]

Made of more than 40 subunits, the rotenone-sensitive NADH:ubiquinone oxidoreductase (complex I) is the most intricate membrane-bound enzyme of the mitochondrial respiratory chain. In vascular plants, fungi, and animals, at least seven complex I subunits (ND1, -2, -3, -4, -4L, -5, and -6; ND is NADH dehydrogenase) are coded by mitochondrial genes. The role of these highly hydrophobic subunits in the enzyme activity and assembly is still poorly understood. In the unicellular green alga Chlamydomonas reinhardtii, the ND3 and ND4L subunits are encoded in the nuclear genome, and we show here that the corresponding genes, called NUO3 and NUO11, respectively, display features that facilitate their expression and allow the proper import of the corresponding proteins into mitochondria. In particular, both polypeptides show lower hydrophobicity compared to their mitochondrion-encoded counterparts. The expression of the NUO3 and NUO11 genes has been suppressed by RNA interference. We demonstrate that the absence of ND3 or ND4L polypeptides prevents the assembly of the 950-kDa whole complex I and suppresses the enzyme activity. The putative role of hydrophobic ND subunits is discussed in relation to the structure of the complex I enzyme. A model for the assembly pathway of the Chlamydomonas enzyme is proposed. [less ▲]

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See detailChromosome localization changes in the Trypanosoma cruzi nucleus.
Elias, M Carolina Q B; Faria, Marcella; Mortara, Renato A et al

in Eukaryotic Cell (2002), 1(6), 944-53

Chromosome localization in the interphase nuclei of eukaryotes depends on gene replication and transcription. Little is known about chromosome localization in protozoan parasites such as trypanosomes ... [more ▼]

Chromosome localization in the interphase nuclei of eukaryotes depends on gene replication and transcription. Little is known about chromosome localization in protozoan parasites such as trypanosomes, which have unique mechanisms for the control of gene expression, with most genes being posttranscriptionally regulated. In the present study, we examined where the chromosomes are replicated in Trypanosoma cruzi, the agent of Chagas' disease. The replication sites, identified by the incorporation of 5-bromodeoxyuridine, are located at the nuclear periphery in proliferating epimastigote forms in the early S phase of the cell cycle. When the S phase ends and cells progress through the cell cycle, 5-bromodeoxyuridine labeling is observed in the nuclear interior, suggesting that chromosomes move. We next monitored chromosome locations in different stages of the cell cycle by using a satellite DNA sequence as a probe in a fluorescence in situ hybridization assay. We found two distinct labeling patterns according to the cell cycle stage. The first one is seen in the G(1) phase, in hydroxyurea-arrested epimastigotes or in trypomastigotes, which are differentiated nondividing forms. In all of these forms the satellite DNA is found in dots randomly dispersed in the nucleus. The other pattern is found in cells from the S phase to the G(2) phase. In these cells, the satellite DNA is found preferentially at the nuclear periphery. The labeling at the nuclear periphery disappears only after mitosis. Also, DNA detected with terminal deoxynucleotidyl transferase is found distributed throughout the nuclear space in the G(1) phase but concentrated at the nuclear periphery in the S phase to the G(2) phase. These results strongly suggest that T. cruzi chromosomes move and, after entering the S phase, become constrained at the nuclear periphery, where replication occurs. [less ▲]

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