Nuclear Export of 60S Ribosomal Subunits Depends on Xpo1p and Requires a Nuclear Export Sequence-Containing Factor, Nmd3p, That Associates with the Large Subunit Protein Rpl10p

Nuclear export of ribosomes requires a subset of nucleoporins and the Ran system, but specific transport factors have not been identified. Using a large subunit reporter (Rpl25p-eGFP), we have isolated several temperature-sensitive ribosomal export (rix) mutants. One of these corresponds to the ribosomal protein Rpl10p, which interacts directly with Nmd3p, a conserved and essential protein associated with 60S subunits. We find that thermosensitive nmd3 mutants are impaired in large subunit export. Strikingly, Nmd3p shuttles between the nucleus and cytoplasm and is exported by the nuclear export receptor Xpo1p. Moreover, we show that export of 60S subunits is Xpo1p dependent. We conclude that nuclear export of 60S subunits requires the nuclear export sequence-containing nonribosomal protein Nmd3p, which directly binds to the large subunit protein Rpl10p

Regulation of Ribosomal RNA Production by RNA Polymerase I: Does Elongation Come First?

Ribosomal RNA (rRNA) production represents the most active transcription in the cell. Synthesis of the large rRNA precursors (35–47S) can be achieved by up to 150 RNA polymerase I (Pol I) enzymes simultaneously transcribing each rRNA gene. In this paper, we present recent advances made in understanding the regulatory mechanisms that control elongation. Built-in Pol I elongation factors, such as Rpa34/Rpa49 in budding yeast and PAF53/CAST in humans, are instrumental to the extremely high rate of rRNA production per gene. rRNA elongation mechanisms are intrinsically linked to chromatin structure and to the higher-order organization of the rRNA genes (rDNA). Factors such as Hmo1 in yeast and UBF1 in humans are key players in rDNA chromatin structure in vivo. Finally, elongation factors known to regulate messengers RNA production by RNA polymerase II are also involved in rRNA production and work cooperatively with Rpa49 in vivo

Periodicity in fields of elongating dunes

Dune fields are commonly associated with periodic patterns that are among the most recognizable landscapes on Earth and other planetary bodies. However, in zones of limited sediment supply, where periodic dunes elongate and align in the direction of the resultant sand flux, there has been no attempt to explain the emergence of such a regular pattern. Here, we show, by means of numerical simulations, that the elongation growth mechanism does not produce a pattern with a specific wavelength. Periodic elongating dunes appear to be a juxtaposition of individual structures, the arrangement of which is due to regular landforms at the border of the field acting as boundary conditions. This includes, among others, dune patterns resulting from bed instability, or the crestline reorganization induced by dune migration. The wavelength selection in fields of elongating dunes therefore reflects the interdependence of dune patterns over the course of their evolution.Comment: 7 pages, 4 figure

Mutations in TFIIH causing trichothiodystrophy are responsible for defects in ribosomal RNA production and processing

The basal transcription/repair factor II H (TFIIH), found mutated in cancer-prone or premature aging diseases, plays a still unclear role in RNA polymerase I transcription. Furthermore, the impact of this function on TFIIHrelated diseases, such as trichothiodystrophy (TTD), remains to be explored. Here, we studied the involvement of TFIIH during the whole process of ribosome biogenesis, from RNAP1 transcription to maturation steps of the ribosomal RNAs. Our results show that TFIIH is recruited to the ribosomal DNA in an active transcription- dependent manner and functions in RNAP1 transcription elongation through ATP hydrolysis of the XPB subunit. Remarkably, we found a TFIIH allele-specific effect, affecting RNAP1 transcription and/or the pre-rRNA maturation process. Interestingly, this effect was observed in mutant TFIIH-TTD cells and also in the brains of TFIIH-TTD mice. Our findings provide evidence that defective ribosome synthesis represents a new faulty mechanism involved in the pathophysiology of TFIIH-related diseases.</p

Mutations in TFIIH causing trichothiodystrophy are responsible for defects in ribosomal RNA production and processing

The basal transcription/repair factor II H (TFIIH), found mutated in cancer-prone or premature aging diseases, plays a still unclear role in RNA polymerase I transcription. Furthermore, the impact of this function on TFIIHrelated diseases, such as trichothiodystrophy (TTD), remains to be explored. Here, we studied the involvement of TFIIH during the whole process of ribosome biogenesis, from RNAP1 transcription to maturation steps of the ribosomal RNAs. Our results show that TFIIH is recruited to the ribosomal DNA in an active transcription- dependent manner and functions in RNAP1 transcription elongation through ATP hydrolysis of the XPB subunit. Remarkably, we found a TFIIH allele-specific effect, affecting RNAP1 transcription and/or the pre-rRNA maturation process. Interestingly, this effect was observed in mutant TFIIH-TTD cells and also in the brains of TFIIH-TTD mice. Our findings provide evidence that defective ribosome synthesis represents a new faulty mechanism involved in the pathophysiology of TFIIH-related diseases.</p

Trans regulation in the Ultrabithorax gene of Drosophila: alterations in the promoter enhance transvection

PMCID: PMC556824We report a genetic and molecular study of UbxMX6 and Ubx195rx1, two mutations in the Ultrabithorax (Ubx) locus which appear to have a strong effect on the activity of the homologous Ubx gene. These mutations show the characteristic embryonic and adult phenotypes of Ubx null alleles, and also fail to produce any detectable Ubx product. Yet, genetic and phenotypic analyses involving a large number of trans heterozygous combinations of UbxMX6 and Ubx195rx1 with different classes of Ubx mutations, indicate that they hyperactivate the homologous gene. This effect is induced on wildtype or mutant forms of Ubx, provided that the pairing in the bithorax region is normal, i.e. these mutations have a strong positive effect on transvection. We also show that, unlike all the other known cases of transvection in Ubx, this is not zeste-dependent. Southern analyses indicate that UbxMX6 is a 3.4 kb deletion, and Ubx195rx1 is an approximately 11 kb insertion of foreign DNA, both in the promoter region. We speculate that the region altered in the mutations may have a wildtype function to ensure cis-autonomy of the regulation of Ubx transcription.This work was supported by grants from the DGICYT and the Fundación Ramón Areces.Peer reviewe

Étude de l'organisation spatiale de la transcription des gènes d'ADN ribosomiques

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Capturing Chromosome Structural Properties From Their Spatial and Temporal Fluctuations

International audienc

Analyse quantitative et fonctionnelle de la dynamique chromosomique (influence du nucléole sur la régulation de l'expression des genes)

Chromatin is distributed non-randomly within the cell nucleus. Its spatial organization has been demonstrated to be important for nuclear metabolism such as, DNA replication, reparation or transcription. I studied the budding yeast HMG-box protein Hmo1. A screen demonstrated that this chromatin-associated protein is genetically linked to the RNA polymerase (Pol) I, to genes coding for ribosomal proteins (RPGs) as well as to genes implicated in stress response. I could show that Hmo1 physically interacts with the rRNA coding gene transcribed by Pol I and with a subset of RPG promoters. Global expression analyses showed a clear dependence on Hmo1 for the expression of a sub-set of RPGs. An hmo1 deletion strain is also largely alleviated in repressing RPG transcription after TOR complex 1 inhibition. These results suggested that Hmo1 is implicated in Pol I transcription as well as RPG regulation. Since Hmo1 is a bona fide nucleolar factor, we wanted to test if Pol II transcribed RPGs associated with Hmo1 are localized in the proximity of the nucleolus. We first developed a new method allowing determination of gene localization probabilities with very high accuracy and with respect to the nucleolus. We could demonstrate by analyzing thousands of cells, that genes are confined into sub-nuclear volumes. These gene territories show a locus specific size and can be remodeled upon transcriptional activation. Applying this new method to Pol II transcribed genes required for ribosome biogenesis, such as the RPGs, indicates that the localization of the gene on the chromatin fiber has important implications for its three dimensional positioning.Au sein du noyau des cellules eucaryotes, la chromatine, support de l information génétique, n est pas distribuée de façon aléatoire. Son organisation spatiale est étroitement liée aux métabolismes nucléaires, tels que la réplication de l ADN, la réparation ou la transcription. J ai étudié la protéine Hmo1, une protéine à boîte HMG de la levure. Grâce à un crible génétique, nous avons pu mettre en évidence que Hmo1 est connecté à l ARN polymérase (Pol) I, aux gènes codant pour des protéines ribosomiques (RPG), ainsi que aux gènes impliqués dans la réponse aux stress. J ai pu montrer que Hmo1 interagit physiquement avec la région transcrite de l ADN ribosomique et avec des promoteurs de RPG. De plus, un mutant hmo1-delta perd la capacité de répression de la transcription des RPG après une inhibition de la voie TORC1. Ca indique que Hmo1 est impliquée dans la régulation de la transcription par la Pol I, ainsi que la régulation de l expression des RPG par des voies de transduction du signal comme la voie TORC1. Hmo1 étant une protéine nucléolaire, nous avons émis l hypothèse d une transcription péri-nucléolaire des RPG chez la levure. Après analyse de plusieurs milliers de cellules, nous avons pu démontrer que, au sein d une population cellulaire, les gènes sont confinés dans des sous-volumes nucléaires appelés territoires géniques . Ces derniers ne sont pas distribués de façon aléatoire, pour certains gènes au moins, peuvent être remodelés en fonction de l activité transcriptionnelle. La localisation de gènes nécessaires à la biogenèse du ribosome, tels que les RPG, semble influencée par leur distance génétique au centromère.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Role of Second-Largest RNA Polymerase I Subunit Zn-Binding Domain in Enzyme Assembly

The second-largest subunits of eukaryal RNA polymerases are similar to the β subunits of prokaryal RNA polymerases throughout much of their lengths. The second-largest subunits from eukaryal RNA polymerases contain a four-cysteine Zn-binding domain at their C termini. The domain is also present in archaeal homologs but is absent from prokaryal homologs. Here, we investigated the role of the C-terminal Zn-binding domain of Rpa135, the second-largest subunit of yeast RNA polymerase I. Analysis of nonfunctional Rpa135 mutants indicated that the Zn-binding domain is required for recruitment of the largest subunit, Rpa190, into the RNA polymerase I complex. Curiously, the essential function of the Rpa135 Zn-binding domain is not related to Zn(2+) binding per se, since replacement of only one of the four cysteine residues with alanine led to the loss of Rpa135 function. Even more strikingly, replacement of all four cysteines with alanines resulted in functional Rpa135