AcrDB Help Page

What are CRISPR-Cas and anti-CRISPR?

CRISPR-Cas stands for clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated (Cas) genes. CRISPR-Cas is an adaptive anti-viral immune mechanism, and widely found in ~50% and ~90% of bacterial and archaeal genomes. Anti-CRISPR (Acr) proteins were first discovered in 2013 in Pseudomonas phages and prophages. As of June 2020, 64 experimentally characterized Acr proteins (42 since 2018 and 17 already in 2020) have been published, and most of the them had been identified with the help of bioinformatics. Notably, very little sequence similarity is found between different Acrs, and most of them do not have any conserved Pfam domains and have no homology to known proteins. More information about anti-CRISPRs can be found in AcrFinder webpage.

Application of Anti-CRISPR in genome editing

As the naturally occurring inhibitors of CRISPR-Cas, Acrs have some clear advantages to be a key component of future’s safer and more controllable CRISPR-Cas genome editing tools. These advantages include: (i) Acr is genetically encodable, (ii) there are numerous choices of Acrs with a high diversity and broad spectrum, (iii) different Acrs target different Cas nucleases with diverse sizes, inhabitation strengths, and mechanisms, and (iv) Acrs can be easily integrated into a variety of existing in vivo and in vitro molecular cloning systems. More information can be found in a recent review paper. Since 2017, over 15 cases have already been published, applying Acrs to finely control CRISPR-Cas gene editing, gene regulation, epigenetic modification, DNA imaging, and gene drive, and more will surely happen with acceleratingly more new Acrs being discovered.

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Windows 10 73.0.3683.86 71.0 44.18362.449.0 n/a


1. Browse database with three entries: (i) browse by Taxonomy | (ii) search by keywords | (iii) browse by Cas subtypes (default)
2. Anti-CRISPR result page:

(i) AcrFinder guilt by association (GBA) result(1) Tabular View | (2) Graphic View | (3) Jbrowse View

(ii) AcrFinder Acr homology search result

(iii) CRISPRCasFinder result

Follow the steps below to learn how to use AcrDB website and understand the data:

Download page

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