The gRAMP CRISPR-Cas effector is an RNA endonuclease complexed with a caspase-like peptidase

Type III CRISPR-Cas immunity is widespread in prokaryotes and is generally mediated by multisubunit effector complexes. These complexes recognize complementary viral transcripts and can activate ancillary immune proteins. Here, we describe a type III-E effector from Candidatus “Scalindua brodae” (Sb-gRAMP), which is natively encoded by a...

Mechanism for Cas4-assisted directional spacer acquisition in CRISPR–Cas

Prokaryotes adapt to challenges from mobile genetic elements by integrating spacers derived from foreign DNA in the CRISPR array¹. Spacer insertion is carried out by the Cas1–Cas2 integrase complex^2–4. A substantial fraction of CRISPR–Cas systems use a Fe–S cluster containing Cas4 nuclease to ensure that spacers are...

Cas4 Facilitates PAM-Compatible Spacer Selection during CRISPR Adaptation

CRISPR-Cas systems adapt their immunological memory against their invaders by integrating short DNA fragments into clustered regularly interspaced short palindromic repeat (CRISPR) loci. While Cas1 and Cas2 make up the core machinery of the CRISPR integration process, various class I and II CRISPR-Cas systems encode Cas4 proteins for which...