AsianScientist (Mar. 11, 2014) – The first high resolution three-dimensional structure of the DNA modifying enzyme Cas9 gives scientists an insight into its function and informs the design of new genetic tools.
CRISPRs (Clustered Regularly Interspaced Short Palindromic Repeats) are short palindromic repeats found in bacterial DNA. CRISPR sequences are transcribed into RNA, which act as a guide for CRISPR-associated or “Cas” proteins, targeting the Cas protein to foreign DNA from viruses or phages. When the targeting RNA matches the foreign DNA, the Cas protein makes a double stranded break in the DNA. This property enables scientists to either disrupt or modify gene function using custom RNA sequences, making it a potentially useful tool for genetic research.
Researchers from the Broad Institute at MIT collaborated with researchers from the University of Tokyo to determine the structural details of a Cas protein, Cas9, in complex with guide RNA and target DNA. Their findings are published in the February 27 issue of Cell.
“We’ve come to view the Cas9 complex as the ultimate ‘guided missile’ that we can use to target precise sites in the genome,” says co-senior author Feng Zhang. “This study provides a schematic of the entire system — it shows the missile (the Cas9 protein), the programming instructions (the guide RNA) that send it to the right location, and the target DNA. It also reveals the secret of how these pieces function together to make the whole system work.”
The detailed structural information provided by the study is required for understanding how RNA-guided Cas9 targets matching DNA sequences and how its specificity can be improved. Furthermore, the authors also reported the creation of a Cas9 truncation mutant that will facilitate Cas9 packaging into size-constrained viral vectors for in vivo and therapeutic applications.
The team is now looking to improve the Cas9 targeting specificity, the in vitro and in vivo delivery, and engineering of Cas9 for novel functions.
The article can be found at: Nishimasu et al. (2014) Crystal Structure of Cas9 in Complex with Guide RNA and Target DNA.
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Copyright: Asian Scientist Magazine; Photo: Broad Institute.
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