Proteomic identification of heterogeneous nuclear ribonucleoprotein L as a novel component of SLM/Sam68 nuclear bodies

Background: Active pre-mRNA splicing occurs co-transcriptionally, and takes place throughout the nucleoplasm of eukaryotic cells. Splicing decisions are controlled by networks of nuclear RNA-binding proteins and their target sequences, sometimes in response to signalling pathways. Sam68 (Src-associated in mitosis 68 kDa) is the prototypic member of the STAR (Signal Transduction and Activation of RNA) family of RNA-binding proteins, which regulate splicing in response to signalling cascades. Nuclear Sam68 protein is concentrated within subnuclear organelles called SLM/Sam68 Nuclear Bodies (SNBs), which also contain some other splicing regulators, signalling components and nucleic acids. Results: We used proteomics to search for the major interacting protein partners of nuclear Sam68. In addition to Sam68 itself and known Sam68-associated proteins (heterogeneous nuclear ribonucleoproteins hnRNP A1, A2/B1 and G), we identified hnRNP L as a novel Sam68-interacting protein partner. hnRNP L protein was predominantly present within small nuclear protein complexes approximating to the expected size of monomers and dimers, and was quantitatively associated with nucleic acids. hnRNP L spatially co-localised with Sam68 as a novel component of SNBs and was also observed within the general nucleoplasm. Localisation within SNBs was highly specific to hnRNP L and was not shared by the closely-related hnRNP LL protein, nor any of the other Sam68-interacting proteins we identified by proteomics. The interaction between Sam68 and hnRNP L proteins was observed in a cell line which exhibits low frequency of SNBs suggesting that this association also takes place outside SNBs. Although ectopic expression of hnRNP L and Sam68 proteins independently affected splicing of CD44 variable exon v5 and TJP1 exon 20 minigenes, these proteins did not, however, co-operate with each other in splicing regulation of these target exons. Conclusion: Here we identify hnRNP L as a novel SNB component. We show that, compared with other identified Sam68-associated hnRNP proteins and hnRNP LL, this co-localisation within SNBs is specific to hnRNP L. Our data suggest that the novel Sam68-hnRNP L protein interaction may have a distinct role within SNBs

Nickel on Lead, Magnetically Dead or Alive?

Two atomic layers of Ni condensed onto Pb films behave, according to anomalous Hall effect measurements, as magnetic dead layers. However, the Ni lowers the superconducting T_{c} of the Pb film. This has lead to the conclusion that the Ni layers are still very weakly magnetic. In the present paper the electron dephasing due to the Ni has been measured by weak localization. The dephasing is smaller by a factor 100 than the pair-breaking. This proves that the T_{c}-reduction in the PbNi films is not due magnetic Ni moments

188Hg, cas limite des noyaux critiques

The γ and e- emitted by 18881Tl (T1/2 = 71 s) nuclei on-line mass separated at ISOCELE (Orsay) have been studied and a partial level scheme of 18880Hg nuclei established. It shows how Hg nuclei of unstable oblate shape become critical nuclei (β2 γβ3 Δ unstable) at A = 186.Le 18880Hg est étudié par conversion interne et émission γ (spectre direct, en coïncidences, et corrélations angulaires) à partir de la désintégration du 188 81Tl (T½ = 71 s) isotopiquement séparé en ligne à ISOCELE (Orsay). En plus d'une bande fondamentale quasi sphérique et d'une bande déformée (O+) déjà vues par ions lourds, une bande γ et une bande de parité négative 5- 7- 6- 8- 9- sont mises en évidence; des états de vibration octupolaire sont suggérés. Cet ensemble montre comment s'effectue la transition entre noyaux de forme aplatie instable et noyaux critiques (β2 γβ 3 Δ instables)