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To equalize X-chromosome dosages between the sexes, the female mammal inactivates one of her two X chromosomes. X-chromosome inactivation (XCI) is initiated by expression of Xist, a 17-kb noncoding RNA (ncRNA) that accumulates on the X in cis. Because interacting factors have not been isolated, the mechanism by which Xist induces silencing remains unknown.(More)
Gene silencing through RNA interference (RNAi) is carried out by RISC, the RNA-induced silencing complex. RISC contains two signature components, small interfering RNAs (siRNAs) and Argonaute family proteins. Here, we show that the multiple Argonaute proteins present in mammals are both biologically and biochemically distinct, with a single mammalian family(More)
Genetic, biochemical and structural studies have implicated Argonaute proteins as the catalytic core of the RNAi effector complex, RISC. Here we show that recombinant, human Argonaute2 can combine with a small interfering RNA (siRNA) to form minimal RISC that accurately cleaves substrate RNAs. Recombinant RISC shows many of the properties of RISC purified(More)
Argonaute proteins and small interfering RNAs (siRNAs) are the known signature components of the RNA interference effector complex RNA-induced silencing complex (RISC). However, the identity of "Slicer," the enzyme that cleaves the messenger RNA (mRNA) as directed by the siRNA, has not been resolved. Here, we report the crystal structure of the Argonaute(More)
RNAi has made an enormous impact on biology in a very short period of time. It became an extraordinarily useful and simple tool for gene silencing, even as its fascinating mechanism was gradually unraveling. Understanding the mechanism of RNAi-related pathways, including both transcriptional and posttranscriptional gene silencing and even processes such as(More)
RISC, the RNA-induced silencing complex, uses short interfering RNAs (siRNAs) or micro RNAs (miRNAs) to select its targets in a sequence-dependent manner. Key RISC components are Argonaute proteins, which contain two characteristic domains, PAZ and PIWI. PAZ is highly conserved and is found only in Argonaute proteins and Dicer. We have solved the crystal(More)
p55 is a common component of many chromatin-modifying complexes and has been shown to bind to histones. Here, we present a crystal structure of Drosophila p55 bound to a histone H4 peptide. p55, a predicted WD40 repeat protein, recognizes the first helix of histone H4 via a binding pocket located on the side of a beta-propeller structure. The pocket cannot(More)
Huntington's disease (HD) is caused by expansion of the polymorphic polyglutamine segment in the huntingtin protein. Full-length huntingtin is thought to be a predominant HEAT repeat alpha-solenoid, implying a role as a facilitator of macromolecular complexes. Here we have investigated huntingtin's domain structure and potential intersection with epigenetic(More)
Argonaute is a key enzyme of various RNA silencing pathways. We use single-molecule fluorescence measurements to characterize the reaction mechanisms of the core-RISC (RNA-induced silencing complex) composed of human Argonaute 2 and a small RNA. We found that target binding of core-RISC starts at the seed region, resulting in four distinct reaction(More)
WDR5 is a component of the mixed lineage leukemia (MLL) complex, which methylates lysine 4 of histone H3, and was identified as a methylated Lys-4 histone H3-binding protein. Here, we present a crystal structure of WDR5 bound to an MLL peptide. Surprisingly, we find that WDR5 utilizes the same pocket shown to bind histone H3 for this MLL interaction.(More)