Researchers at the Whitehead Institute and Memorial Sloan-Kettering Cancer Center have defined and analyzed the crystal structure of a yeast Argonaute protein bound to RNA. This complex plays a key role in the RNA interference (RNAi) pathway that silences gene expression. Describing the molecular structure of a eukaryotic Argonaute protein has been a goal of the RNAi field for close to a decade. "You can learn a lot from biochemical experiments, but to more fully understand a protein like Argonaute, it's useful to know where all of the atoms are and which amino acids are playing important roles," says Whitehead Institute Member Dr. David Bartel, who is also an MIT professor of biology and a Howard Hughes Medical Institute (HHMI) investigator. "Learning the Argonaute crystal structure is an important step in understanding the RNAi biochemical pathway and will be the basis for many future experiments." The yeast Argonaute structure is described in the June 21, 2012 issue of Nature. In humans and most other eukaryotes, the RNAi pathway can reduce cellular protein production by reducing the proteins' RNA templates. By exploiting this pathway, scientists are able to knock down the expression of specific proteins and thereby determine their roles within the cell or organism. The RNAi pathway has also been of considerable interest for the treatment of human disease. RNAi depends on two proteins, Dicer and Argonaute. Dicer recognizes double-stranded RNA (dsRNA), latches onto it, and chops it into pieces 21-23 nucleotides long. Argonaute recognizes the dsRNA bits, discards one strand, and uses the other as a guide. When a single-stranded RNA matches the guide RNA's sequence, Argonaute cleaves the targeted RNA, thereby preventing it from serving as a template for protein production.
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