GRSF1 regulates RNA processing in mitochondrial RNA granules.

Various specialized domains have been described in the cytosol and the nucleus; however, little is known about compartmentalization within the mitochondrial matrix. GRSF1 (G-rich sequence factor 1) is an RNA binding protein that was previously reported to localize in the cytosol. We found that an isoform of GRSF1 accumulates in discrete foci in the mitochondrial matrix. These foci are composed of nascent mitochondrial RNA and also contain RNase P, an enzyme that participates in mitochondrial RNA processing. GRSF1 was found to interact with RNase P and to be required for processing of both classical and tRNA-less RNA precursors. In its absence, cleavage of primary RNA transcripts is abnormal, leading to decreased expression of mitochondrially encoded proteins and mitochondrial dysfunction. Our findings suggest that the foci containing GRSF1 and RNase P correspond to sites where primary RNA transcripts converge to be processed. We have termed these large ribonucleoprotein structures "mitochondrial RNA granules.

2^2H (3^3He,t) 2p reaction at 2 GeV

E

Modelling spectral and timing properties of accreting black holes: the hybrid hot flow paradigm

The general picture that emerged by the end of 1990s from a large set of optical and X-ray, spectral and timing data was that the X-rays are produced in the innermost hot part of the accretion flow, while the optical/infrared (OIR) emission is mainly produced by the irradiated outer thin accretion disc. Recent multiwavelength observations of Galactic black hole transients show that the situation is not so simple. Fast variability in the OIR band, OIR excesses above the thermal emission and a complicated interplay between the X-ray and the OIR light curves imply that the OIR emitting region is much more compact. One of the popular hypotheses is that the jet contributes to the OIR emission and even is responsible for the bulk of the X-rays. However, this scenario is largely ad hoc and is in contradiction with many previously established facts. Alternatively, the hot accretion flow, known to be consistent with the X-ray spectral and timing data, is also a viable candidate to produce the OIR radiation. The hot-flow scenario naturally explains the power-law like OIR spectra, fast OIR variability and its complex relation to the X-rays if the hot flow contains non-thermal electrons (even in energetically negligible quantities), which are required by the presence of the MeV tail in Cyg X-1. The presence of non-thermal electrons also lowers the equilibrium electron temperature in the hot flow model to <100 keV, making it more consistent with observations. Here we argue that any viable model should simultaneously explain a large set of spectral and timing data and show that the hybrid (thermal/non-thermal) hot flow model satisfies most of the constraints.Comment: 26 pages, 13 figures. To be published in the Space Science Reviews and as hard cover in the Space Sciences Series of ISSI - The Physics of Accretion on to Black Holes (Springer Publisher

Mitochondrial RNA granules: Compartmentalizing mitochondrial gene expression.

In mitochondria, DNA replication, gene expression, and RNA degradation machineries coexist within a common nondelimited space, raising the question of how functional compartmentalization of gene expression is achieved. Here, we discuss the recently characterized "mitochondrial RNA granules," mitochondrial subdomains with an emerging role in the regulation of gene expression

ETUDE DES INTERACTIONS DANS L'ETAT FINAL DANS LES REACTIONS DE TRANSFERT 3He(d, t)2p, 3He(d, 3He)pn, 3H(d, 3H)pn, 3H(d, 3He)2n à 82 MeV DETERMINATION DE ann

Les spectres d'intéraction dans l'état final ont été mesurés à 2° 1/2 et à 7° 1/2 dans ces quatre réactions. L'étude des spectres permet : - de vérifier la validité du formalisme de Watson-Migdal permettant d'extraire la longueur de diffusion nucléon-nucléon car la longueur de diffusion pp intervenant dans la première réaction est bien connue par ailleurs. Les approximations dans le formalisme devraient être d'autant meilleures que l'énergie incidente est plus grande. Or on constate qu'il faut tenir compte d'une variation de l'élément de matrice de la réaction primaire en fonction de l'énergie de la particule détectée. - d'obtenir de l'analyse des spectres de la réaction 3H(d, 3He)2n les valeurs des paramètres ann et ron. - de comparer les sections efficaces de ces réactions isobares, qui paraissent effectivement être dans les rapports attendus pour des réactions miroir deux à deux.Final state interaction spectra have been measured at 2° 1/2 and 7° 1/2 in the reactions 3He(d, t)2p ; 3He(d, 3He)pn ; 3H(d, t)pn and 3H(d, 3He)2n at 82 MeV. The study of these spectra allows : - to test the validity of the Watson-Migdal formalism which permits the extraction of the nucleon-nucleon scattering length, the pp scattering length intervening in the first of these reactions being well known. The Watson-Migdal approximations should be better at high primary energies. It appears necessary to take into account a variation of the primary reaction matrix element with the energy of the outgoing observed particle. - to obtain the values of ann and ron from the analysis of the energy spectra of the 3H(d, 3He)2n reaction. - to compare the cross-sections of these two pairs of mirror reactions, which appear effectively to correspond to the expected ratios