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HIV-1 Rev protein directs nuclear export of pre-mRNAs and mRNAs containing its binding site, the Rev response element (RRE). To define how Rev acts, we used conjugates between bovine serum albumin (BSA) and peptides comprising the Rev activation domain (BSA-R). BSA-R inhibited Rev-mediated nuclear RNA export, whereas a mutant activation domain peptide(More)
Small interfering RNAs (siRNAs) are the mediators of mRNA degradation in the process of RNA interference (RNAi). Here, we describe a human biochemical system that recapitulates siRNA-mediated target RNA degradation. By using affinity-tagged siRNAs, we demonstrate that a single-stranded siRNA resides in the RNA-induced silencing complex (RISC) together with(More)
mRNP remodeling events required for the transition of an mRNA from active translation to degradation are currently poorly understood. We identified protein factors potentially involved in this transition, which are present in mammalian P bodies, cytoplasmic foci enriched in 5' --> 3' mRNA degrading enzymes. We demonstrate that human P bodies contain the(More)
The box C/D snoRNAs function in directing 2'-O-methylation and/or as chaperones in the processing of ribosomal RNA. We show here that Snu13p (15.5 kD in human), a component of the U4/U6.U5 tri-snRNP, is also associated with the box C/D snoRNAs. Indeed, genetic depletion of Snu13p in yeast leads to a major defect in RNA metabolism. The box C/D motif can be(More)
In eukaryotic cells, freshly synthesized messenger RNA (pre-mRNA) contains stretches of non-coding RNA that must be excised before the RNA can be translated into protein. Their removal is catalysed by the spliceosome, a large complex formed when a number of small nuclear ribonucleoprotein particles (snRNPs) bind sequentially to the pre-mRNA. The first snRNP(More)
The U1, U2, U4/U6, and U5 small nuclear ribonucleoprotein particles (snRNPs) involved in pre-mRNA splicing contain seven Sm proteins (B/B', D1, D2, D3, E, F, and G) in common, which assemble around the Sm site present in four of the major spliceosomal small nuclear RNAs (snRNAs). These proteins share a common sequence motif in two segments, Sm1 and Sm2,(More)
In the assembly of a prespliceosome, U2 small nuclear ribonucleoprotein (snRNP) functions in pre-messenger RNA (mRNA) splicing together with splicing factors (SFs) 3a, SF3b, and several other proteins. The 17S but not the 12S form of U2 snRNP is active in splicing-complex formation. Here it is shown that the SF3a subunits correspond to three of the 17S U2(More)
RNA silencing processes are guided by small RNAs known as siRNAs and microRNAs (miRNAs) . They reside in ribonucleoprotein complexes, which guide the cleavage of complementary mRNAs or affect stability and translation of partial complementary mRNAs . Argonaute (Ago) proteins are at the heart of silencing effector complexes and bind the single-stranded siRNA(More)
Exactly how specific splice sites are recognized during the processing of complex precursor messenger RNAs is not clear. Small nuclear ribonucleoprotein particles (snRNPs) are involved, but are not sufficient by themselves to define splice sites. Now a human protein essential for splicing in vitro, called alternative splicing factor/splicing factor 2, is(More)
Mammalian cells contain a highly specific terminal uridylyl transferase (TUTase) that exclusively accepts U6 snRNA as substrate. This enzyme, termed U6-TUTase, was purified from HeLa cell extracts and analyzed by microsequencing. All sequenced peptides matched a unique human cDNA coding for a previously unknown protein. Domain structure analysis revealed(More)