Methods For High Signal-To-Noise Imaging Of Chromosomal Loci In Cells Using Fluorescent Cas9

Cas9 is an endonuclease that binds complementary target DNA and generates site-specific breaks using two conserved nuclease domains. By inactivating both nuclease domains, dCas9 is produced, which functions as a programmable DNA binding protein. Current methods use dCas9-GFP fusions to image chromosomal loci, but have insufficient signal-to-noise ratio and often misidentify loci. UC Berkeley researchers have engineered a Cas9 variant that can be labeled with small molecule fluorescent dyes. This variant utilizes a conformational change in Cas9 to provide highly specific identification of chromosomal loci, and has been shown to work in a proof-of-principle experiment using Förster resonance energy transfer (FRET) pairs. Terri Sale terri.sale@berkeley.edu 510-643-4219