An intact Box C sequence in the U3 snRNA is required for binding of fibrillarin, the protein common to the major family of nucleolar snRNPs.
ABSTRACT The mammalian U3 snRNP is one member of a recently described family of nucleolar snRNPs which also includes U8, U13, U14, X and Y. All of these snRNPs are immunoprecipitable by anti-fibrillarin autoantibodies, suggesting the existence of a common binding site for the 34 kDa fibrillarin (Fb) protein. Two short nucleotide sequences, called Boxes C and D, present in each of these RNAs are the most likely sites for fibrillarin binding. We have developed a HeLa in vitro assembly system for binding of fibrillarin to human U3 snRNA. Reconstitution of the input RNA is specific in our assay since four of the other nucleolar small RNAs (U8, U13, X and Y) which have Boxes C and D become immunoprecipitable by anti-fibrillarin whereas two RNAs which lack these sequences (5S and 5.8S) do not. Deletion analyses of the U3 snRNA demonstrate that the presence of Box C but not Box D is required for fibrillarin binding. Moreover, seven single or double site-specific mutations in the U3 Box C abolish binding. The role of the Box C-fibrillarin interaction in the biogenesis of the Fb snRNPs is discussed.
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ABSTRACT: Since preventive treatments for prion disease require early identification of subjects at risk, we searched for surrogate peripheral markers characterizing the asymptomatic phases of such conditions. To this effect, we subjected blood mRNA from E200K PrP CJD patients and corresponding family members to global arrays and found that the expression of Snord3A, a non-coding RNA transcript, was elevated several times in CJD patients as compared to controls, while asymptomatic carriers presented intermediate Snord3A levels. In the brains of TgMHu2ME199K mice, a mouse model mimicking for E200K CJD, Snord 3A levels were elevated in an age and disease severity dependent manner, as was the case for brains of these mice in which disease was exacerbated by copper administration. Snord3A expression was also elevated in scrapie infected mice, but not in PrP(0/0) mice, indicating that while the expression levels of this transcript may reflect diverse prion etiologies, they are not related to the loss of PrP(C)'s function. Elevation of Snord3A was consistent with the activation of ATF6, representing one of the arms of the unfolded protein response system. Indeed, SnoRNAs were associated with reduced resistance to oxidative stress, and with ER stress in general, factors playing a significant role in this and other neurodegenerative conditions. We hypothesize that in addition to its function as a disease marker, Snord3A may play an important role in the mechanism of prion disease manifestation and progression.PLoS ONE 01/2013; 8(1):e54433. DOI:10.1371/journal.pone.0054433 · 3.53 Impact Factor
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ABSTRACT: Cajal bodies (CBs) are subnuclear organelles that contain components of a number of distinct pathways in RNA transcription and RNA processing. CBs have been linked to other subnuclear organelles such as nucleoli, but the reason for the presence of nucleolar proteins such as fibrillarin in CBs remains uncertain. Here, we use full-length fibrillarin and truncated fibrillarin mutants fused to green fluorescent protein (GFP) to demonstrate that specific structural domains of fibrillarin are required for correct intranuclear localization of fibrillarin to nucleoli and CBs. The second spacer domain and carboxy terminal alpha-helix domain in particular appear to target fibrillarin, respectively, to the nucleolar transcription centers and CBs. The presence of the RNP domain seems to be a prerequisite for correct targeting of fibrillarin. Time-lapse confocal microscopy of human cells that stably express fibrillarin-GFP shows that CBs fuse and split, albeit at low frequencies. Recovered fluorescence of fibrillarin-GFP in nucleoli and CBs after photobleaching indicates that it is highly mobile in both organelles (estimated diffusion constant ∼0.02 μm2 s−1), and has a significantly larger mobile fraction in CBs than in nucleoli.The Journal of Cell Biology 10/2000; 151(3):653-662. DOI:10.1083/jcb.151.3.653 · 9.69 Impact Factor
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ABSTRACT: Aquarius is a multifunctional putative RNA helicase that binds precursor-mRNA introns at a defined position. Here we report the crystal structure of human Aquarius, revealing a central RNA helicase core and several unique accessory domains, including an ARM-repeat domain. We show that Aquarius is integrated into spliceosomes as part of a pentameric intron-binding complex (IBC) that, together with the ARM domain, cross-links to U2 snRNP proteins within activated spliceosomes; this suggests that the latter aid in positioning Aquarius on the intron. Aquarius's ARM domain is essential for IBC formation, thus indicating that it has a key protein-protein-scaffolding role. Finally, we provide evidence that Aquarius is required for efficient precursor-mRNA splicing in vitro. Our findings highlight the remarkable structural adaptations of a helicase to achieve position-specific recruitment to a ribonucleoprotein complex and reveal a new building block of the human spliceosome.Nature Structural & Molecular Biology 01/2015; DOI:10.1038/nsmb.2951 · 11.63 Impact Factor