Figure 1.

Prediction of novel target selectors in Tn7-like transposons

(A) Schematic of Tn7 transposition. TnsB (cyan) recognizes both ends (R, right and L, left) and excises the transposon with the help of TnsA (yellow). TnsD is a sequence-specific target selector and binds an attachment site in the bacterial genome to recruit TnsC (orange) and the transposon for insertion.

(B) Pipeline for discovery of novel target selectors. Sequence databases were mined for Tn7 component seeds and searched for genomic co-localization of these seeds. The genomic neighborhoods of the detected loci were annotated, with the focus on cas effectors and genes that appear to be operonized with tnsC and tniQ/tnsD.

(C) Locus architectures of known systems and novel systems identified in this study. Mu (muA and muB) and IS21 (istA and istB) encode relatives of TnsB and TnsC. IS21 has not been reported to be associated with a target selector. Tn7 encodes various target selectors including TniQ/TnsD, TnsE, and Cas effectors (Cas12k, Cascade I-F, and Cascade I-B, which all partner with TniQ), the latter of which constitute CAST systems. We found a novel CAST system containing Cascade I-D and a novel target selector we named TnsF. We also found a TnsF-like target selector in a distinct non-Tn7 transposon.