Usually when you think of the immune system it isn’t at the level of our bacterial friends. But “prokaryotes have evolved diverse RNA-mediated systems that use short CRISPR RNAs (crRNAs) and Cas (CRISPR-associated) proteins to detect and defend against invading DNA elements” This system, also known as the CRISPR/Cas system, is a prokaryotic immune system analogue that is being adapted to engineer eukaryotic genomes in a new technology dubbed CRISPR Interference (CRISPRi).
So far CRISPR/Cas has shown great potential as it can work better than other methods, is easier to use, and is starting to be applied to model organisms. However, a talented group from UCSF has teamed up with some of the pioneers to show that we’ve only seen the tip of the iceberg when it comes to CRISPRs potential, by inventing and deploying the CRISPRi system to repress transcription without altering sequence. Once they gave it a try, here’s what they observed:
- Using the “the CRISPR- associated catalytically inactive dCas9 protein” they created a general platform to target custom RNA sequences to DNA sequences of interest.
- It works in both human and yeast cells.
- The site of delivery is “determined solely by a co-expressed short guide (sg)RNA” which can be custom made to a DNA sequence of interest.
- RNA-seq analysis indicated that this novel “CRISPRi” system shows highly specific transcriptional repression and “minimal off-target effects”.
Given the high level of specificity observed it appears that this system has a crisp leg-up over RNAi and other competing technologies, which aren’t as picky with their targets. The authors conclude that the “results establish that the CRISPR system can be used as a modular and flexible DNA-binding platform for the recruitment of proteins to a target DNA sequence, revealing the potential of CRISPRi as a general tool for the precise regulation of gene expression in eukaryotic cells.”
Read all about it in Cell, July 2013