Structural basis of a Tn7-like transposase recruitment and DNA loading to CRISPR-Cas surveillance complex

摘要

Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and CRISPR-associated (Cas) systems confer RNA-guided adaptive immunity against invading genetic elements in prokaryotic cells.1 These systems employ CRISPR RNA (crRNA) containing surveillance complexes for sequence-specific recognition and degradation of foreign DNA or RNA. Several nuclease-deficient type I-F, I-B, and V-K systems have been reported to be evolutionarily and functionally associated with Tn7-like transposons lacking a key gene for DNA targeting, implying a new mode of RNA-guided DNA insertion.2,3 Recent studies characterized CRISPR-associated transposase in type I-F and V-K systems and established genome-wide programmable site-specific DNA transposition in E. coli cells, providing the prospect of genome editing strategy without requirement of double-strand breaks and endogenous DNA repair pathways.4,5 All these CRISPR-associated transposons contain transposase subunits, CRISPR effector, and a CRISPR array. Furthermore, subunit TniQ, a homolog of E. coli TnsD, forms a stable complex with Vibrio cholerae Tn6677 type I-F effector Cascade (also called Csy complex) and plays an essential role during DNA insertion.