The promise of CRISPR-associated transposons for bacterial functional genomics.

CRISPR-associated transposons (CASTs) are naturally occurring amalgamations of CRISPR-Cas machinery and Tn7-like transposons that direct site-specific integration of transposon DNA via programmable guide RNAs. Although the mechanisms of CAST-based transposition have been well studied at the molecular and structural level, CASTs have yet to be broadly applied to bacterial genome engineering and systematic gene phenotyping (i.e. functional genomics) - likely due to their relatively recent discovery. Here, we describe the function and applications of CASTs, focusing on well-characterized systems, including the type I-F CAST from Vibrio cholerae (VcCAST) and type V-K CAST from Scytonema hofmanni (ShCAST). Further, we discuss the potentially transformative impact of targeted transposition on bacterial functional genomics by proposing genome-scale extensions of existing CAST tools.