The Cas4-Cas1-Cas2 complex mediates precise prespacer processing during CRISPR adaptation.
Elife
; 82019 04 30.
Article
en En
| MEDLINE
| ID: mdl-31021314
ABSTRACT
CRISPR adaptation immunizes bacteria and archaea against viruses. During adaptation, the Cas1-Cas2 complex integrates fragments of invader DNA as spacers in the CRISPR array. Recently, an additional protein Cas4 has been implicated in selection and processing of prespacer substrates for Cas1-Cas2, although this mechanism remains unclear. We show that Cas4 interacts directly with Cas1-Cas2 forming a Cas4-Cas1-Cas2 complex that captures and processes prespacers prior to integration. Structural analysis of the Cas4-Cas1-Cas2 complex reveals two copies of Cas4 that closely interact with the two integrase active sites of Cas1, suggesting a mechanism for substrate handoff following processing. We also find that the Cas4-Cas1-Cas2 complex processes single-stranded DNA provided in cis or in trans with a double-stranded DNA duplex. Cas4 cleaves precisely upstream of PAM sequences, ensuring the acquisition of functional spacers. Our results explain how Cas4 cleavage coordinates with Cas1-Cas2 integration and defines the exact cleavage sites and specificity of Cas4.
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Base de datos:
MEDLINE
Asunto principal:
Bacillus
/
ADN de Cadena Simple
/
Endodesoxirribonucleasas
/
Proteínas Asociadas a CRISPR
Idioma:
En
Revista:
Elife
Año:
2019
Tipo del documento:
Article