The CRISPR-Cas system in E. coli K-12 is considered inactive. We questioned whether mobile elements encode anti-CRISPRs against this system and found a highly abundant AcrIE9-AcrIE10 tandem and a novel AcrIE13 — an HTH protein more similar to Aca than known Acrs. www.pnas.org/doi/10.1073/...
A census of anti-CRISPR proteins reveals AcrIE9 and AcrIE13 as inhibitors of the Escherichia coli K12 type IE CRISPR-Cas system | PNASCRISPR-Cas adaptive immunity systems provide defense against mobile genetic elements
and are often countered by diverse anti-CRISPR (Acr) proteins....www.pnas.org