Spinal muscular atrophy (SMA) is a common neurodegenerative disease that is caused by deletions or loss-of-function mutations in the Survival of Motor Neuron (SMN) protein. SMN is part of a large complex that functions in the assembly/restructuring of ribonucleoprotein (RNP) complexes. We recently showed in HeLa cells that two components of the SMN complex, Gemin3 and Gemin4, together with the argonaute protein eIF2C2, also associate with microRNAs (miRNAs) as part of a novel class of RNPs termed miRNPs. Here we report on miRNPs isolated from neuronal cell lines of mouse and human, and describe 53 novel miRNAs. Several of these miRNAs are conserved in divergent organisms, including rat, zebrafish, pufferfish, and the nematode Caenorhabditis elegans. The chromosomal locations of most of the novel miRNAs were identified and indicate some phylogenetic conservation of the likely precursor structures. Interestingly the gene locus of one miRNA, miR-175, is a candidate region for two neurologic diseases: early-onset parkinsonism (Waisman syndrome) and X-linked mental retardation (MRX3). Also, several miRNAs identified as part of miRNPs in these cells appear to constitute two distinct subfamilies. These subfamilies comprise multiple copies of miRNAs on different chromosomes, suggesting an important function in the regulation of gene expression.

The structure of benzene deposited on a Cu(111) surface has been investigated by a combination of temperature-programmed desorption (TPD), high-resolution electron energy loss spectroscopy (HREELS), and near-edge x-ray absorption fine structure (NEXAFS) measurements. The results indicate that benzene forms a stable bilayer on Cu(ll1) at 110 K prior to multilayer formation. The TPD studies show that the second layer benzene desorbs with a peak temperature 5 K higher than that for benzene multilayers. HREELS and NEXAFS results indicate that benzene in the first layer bonds with its T ring parallel to the surface. With increasing coverage, benzene forms a second layer with its GT ring significantly tilted away from the surface. The results are consistent with an approximately perpendicular configuration between the first and second layer benzene molecules, which is analogous to the structure of crystalline benzene. Isotope labeling experiments indicate there is almost complete mixing between molecules in different layers during sequential adsorption at 110 K.

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The adsorption and reactions of vinyl bromide and vinyl iodide on a Cu(100) surface have been studied by temperature-programmed desorption in conjunction with near-edge X-ray absorption fine structure (NEXAFS) and work function change measurements. Vinyl bromide adsorbs molecularly on the surface at 100 K. The polarization dependence of the π*CC resonance indicates that the molecules lie with their π bond within 28 ± 5° of parallel to the surface. Upon heating, both vinyl bromide and vinyl iodide decompose to generate surface vinyl groups, which adopt a tilted orientation on the surface. Both the molecular halides and the surface vinyl groups show a splitting of the π*CC NEXAFS resonance due to the inequivalence of the carbon atoms in these species. The position of the σ*CC shape resonances for these species indicates little change (<0.05 Å) in CC bond length due to adsorption and dissociation to form vinyl groups. Chemical displacement studies show that the CBr bond cleavage in vinyl bromide occurs at 160 K. This dissociation temperature is confirmed by complementary NEXAFS and work function change measurement results. At 250 K, vinyl groups couple to yield 1,3-butadiene with 100% selectivity.