Citation: Huang et al., doi:10.1093/nar/gkaa857 2020

What are Acr and Aca?

Acr (anti-CRISPR) proteins are short proteins usually found in phages/prophages and other mobile genetic elements that can turn off the CRISPR-Cas system of their prokaryotic hosts. Therefore they were considered as "naturally occurring off-switch" of CRISPR-Cas and having great potential to serve as regulators/modulators of CRISPR-Cas tools for safer and more controllable genome editing.

Acr encoding genes often have an immediate downstream gene coding for a putative transcription regulator named Aca (Acr associated) protein. Published Aca proteins all have a Pfam HTH (helix-turn-helix) domain. The Acr-Aca operon is also known as Acr-Aca locus.

Please see the FAQ page of AcrFinder for more detailed intro to anti-CRISPRs.

Introduction to AcrDB

AcrDB is a database of computationally predicted anti-CRISPR (Acr) and Acr-associated (Aca) operon database. See the Statistics page for details. Similar online databases include Anti-CRISPRdb, CRISPRminer, and AcrCatalog. Compared to these previous databases, AcrDB has the following unique features and data:

  1. It is a genome-scale database with the largest collection of data (39,799 Acr-Aca operons containing Aca or Acr homologs);
  2. It offers a user-friendly web interface with various functions for browsing, graphically viewing, searching, and batch downloading Acr-Aca operons;
  3. It focuses on the genomic context of Acr and Aca candidates instead of individual Acr protein family;
  4. It collects data with three independent programs (AcrFinder and AcRanker and PaCRISPR) each having a unique data mining algorithm for cross validation.