The Future of Gene-Editing
Timeline
Discovery of CRISPR and its Function (1993-2005)
Francisco Mojica was the first to characterize a CRISPR locus and it led him to hypothesize that CRISPR is an adaptive immune system.
Discovery of Cas9 and PAM (May, 2005)
Alexander Bolotin revealed an unusual CRISPR locus that lacked some of the known Cas genes and contained novel Cas genes (Cas9). The spacers had homology to viral genes that share share a common sequence at one end; the sequence protospacer adjacent motif (PAM) was required for target recognition.
Hypothetical Scheme of Adaptive Immunity (March, 2006)
Eugene Koonin proposed a hypothetical scheme for CRISPR cascades as bacterial immune system based on insert structure to bacteriophage DNA in the natural spacer array.
Experiment of Adaptive Immunity (March, 2007)
Spacer Sequences Transcribe into Guide RNAs (August, 2008)
Scientists at Danisco showed that CRISPR systems are an adaptive immune system and they also showed that Cas9 is most likely the only protein that is required for interference.
John van der Oost and colleagues showed that spacer sequences are transcribed into small RNAs to guide Cas proteins to target DNA.
CRISPR Acts on DNA Targets (December, 2008)
Luciano Marraffini and Erik Sontheimer demonstrated how the target molecule was DNA not RNA but it should be noted that a different type of CRISPR system can target RNA.
Cas9 Cleaves Target DNA (December, 2010)
Sylvain Moineau demonstrated that Crispr-Cas9 creates double-stranded breaks in the target DNA at precise positions (3 nucleotides upstream of the PAM). They also confirmed that Cas9 is the only protein required for cleavage in the Crispr-Cas9 system.