Electrical conduction through molecules depends critically on the delocalization of the molecular electronic orbitals and their connection to the metallic contacts. Thiolated (- SH) conjugated organic molecules are therefore considered good candidates for molecular conductors: in such molecules, the orbitals are delocalized throughout the molecular backbone, with substantial weight on the sulphur-metal bonds. However, their relatively small size, typically approximately 1 nm, calls for innovative approaches to realize a functioning single-molecule device. Here we report an approach for contacting a single molecule, and use it to study the effect of localizing groups within a conjugated molecule on the electrical conduction. Our method is based on synthesizing a dimer structure, consisting of two colloidal gold particles connected by a dithiolated short organic molecule, and electrostatically trapping it between two metal electrodes. We study the electrical conduction through three short organic molecules: 4,4'-biphenyldithiol (BPD), a fully conjugated molecule; bis-(4-mercaptophenyl)-ether (BPE), in which the conjugation is broken at the centre by an oxygen atom; and 1,4-benzenedimethanethiol (BDMT), in which the conjugation is broken near the contacts by a methylene group. We find that the oxygen in BPE and the methylene groups in BDMT both suppress the electrical conduction relative to that in BPD.

The COP9 signalosome (CSN) puri®ed from human erythrocytes possesses kinase activity that phosphorylates proteins such as c-Jun and p53 with consequence for their ubiquitin (Ub)-dependent degradation. Here we show that protein kinase CK2 (CK2) and protein kinase D (PKD) co-purify with CSN. Immunoprecipitation and far-western blots reveal that CK2 and PKD are in fact associated with CSN. As indicated by electron microscopy with gold-labeled ATP, at least 10% of CSN particles are associated with kinases. Kinase activity, most likely due to CK2 and PKD, co-immunoprecipitates with CSN from HeLa cells. CK2 binds to DCSN3(111±403) and CSN7, whereas PKD interacts with full-length CSN3. CK2 phosphorylates CSN2 and CSN7, and PKD modi®es CSN7. Both CK2 and PKD phosphorylate c-Jun as well as p53. CK2 phosphorylates Thr155, which targets p53 to degradation by the Ub system. Curcumin, emodin, DRB and resveratrol block CSN-associated kinases and induce degradation of c-Jun in HeLa cells. Curcumin treatment results in elevated amounts of c-Jun±Ub conjugates. We conclude that CK2 and PKD are recruited by CSN in order to regulate Ub conjugate formation.

No abstract

Almost every protein-coding gene undergoes pre-mRNA splicing, and the majority of these pre-mRNAs are alternatively spliced. Alternative exon usage is regulated by the transient formation of protein complexes on the pre-mRNA that typically contain heterogeneous nuclear ribonucleoproteins (hnRNPs). Here we characterize hnRNP G, a member of the hnRNP class of proteins. We show that hnRNP G is a nuclear protein that is expressed in different concentrations in various tissues and that interacts with other splicing regulatory proteins. hnRNP G is part of the supraspliceosome, where it regulates alternative splice site selection in a concentrationdependent manner. Its action on alternative exons can occur without a functional RNA-recognition motif by binding to other splicing regulatory proteins. The RNA-recognition motif of hnRNP G binds to a loose consensus sequence containing a CC(A/C) motif, and hnRNP G preferentially regulates alternative exons where this motif is clustered in close proximity. The X-chromosomally encoded hnRNP G regulates different RNAs than its Y-chromosomal paralogue RNA-binding motif protein, Y-linked (RBMY), suggesting that differences in alternative splicing, evoked by the sexspecific expression of hnRNP G and RBMY, could contribute to molecular sex differences in mammals.All protein-coding genes undergo pre-mRNA processing, and the large majority of these genes are alternatively spliced (1). Alternative exons can change many functional aspects of mRNAs and their encoded proteins. The best understood functions are stop codons or frameshifts that are introduced by 20 -35% of alternative exons, which often destine the altered mRNA to nonsense-mediated decay. Examples described in the literature show that alternative splicing regulates the binding properties, intracellular localization, enzymatic activity, protein stability, and post-translational modifications of a large number of proteins (reviewed in Ref.2). Thus, it appears that alternative pre-mRNA processing is a key mechanism regulating the gene expression of complex organisms by generating multiple mRNA isoforms, which encode functionally diverse proteins. Despite its importance, the exact mechanisms governing splice site selection are still poorly understood. In vertebrate systems, protein complexes assemble transiently on exons, and their interaction with the splicing machinery as well as RNA-RNA interactions between spliceosomal proteins and pre-mRNA determine whether an exon is included or skipped (reviewed in Refs. 3 and 4).When isolated from nuclei of mammalian cells, RNA polymerase II transcripts are found assembled in large ribonucleoprotein 21-MDa complexes, the supraspliceosome, composed of all five spliceosomal small nuclear ribonucleoproteins as well as additional proteins. The entire repertoire of nuclear pre-mRNAs, independent of their length or number of introns, is individually found assembled in supraspliceosomes (reviewed in Ref. 5). Structural studies revealed that the supraspliceosome is composed of four substructure...

We present a self-assembly method to construct CdSe/ZnS quantum dot-gold nanoparticle complexes. This method allows us to form complexes with relatively good control of the composition and structure that can be used for detailed study of the exciton-plasmon interactions. We determine the contribution of the polarization-dependent near-field enhancement, which may enhance the absorption by nearly two orders of magnitude and that of the exciton coupling to plasmon modes, which modifies the exciton decay rate.