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/...
CRISPR-Cas adaptive immunity systems provide defense against mobile genetic elements
and are often countered by diverse anti-CRISPR (Acr) proteins....
