IS200/IS605 Family-Associated TnpB Increases Transposon Activity and Retention

Abstract

ABSTRACTThe IS200/IS605 family are abundant insertion sequences associated with one of the most numerous genes in nature,tnpB. Sequence homologies suggest that transposon-borne TnpB may be an evolutionary precursor to CRISPR-Cas system effector proteins, and TnpB has been shown to function as a Cas-like programmable DNA endonuclease. However, the role of TnpB in transposition and its contributions to genome dynamics remain elusive. Using a suite of fluorescent reporters coupled to transposition, we show that TnpB increases IS608-transposon activity and prevents transposon loss from genomes. Analyzing our results through a mathematical model of transposon dynamics, we discuss the multifaceted roles TnpB may play in transposon regulation. The mutually beneficial transposon-TnpB interaction may explain the prevalence oftnpB, creating conditions for the proliferation and appropriation of TnpB’s RNA-guided endonuclease activity for adaptive immunity.