The evolution of RNA-guided DNA-binding proteins, called TldRs (TnpB-like nuclease-dead repressors), from transposon-encoded TnpB nucleases was investigated in a recent study by Wiegand et al. The researchers identified multiple independent TldR clades that evolved via RuvC active site deterioration and acquired new gene associations. TldRs operate with adjacently encoded non-coding guide RNAs to target complementary DNA sequences flanked by a TAM within promoter regions, downregulating gene expression through competitive exclusion of RNA polymerase.

The study focused on flagellin (FliC)-associated TldR homologues exploited by prophages to remodel the host flagellar apparatus. Utilising in vivo genetic perturbation experiments in a clinical Enterobacter isolate, the researchers demonstrated that TldRs repress host fliC expression while allowing expression of a phage-encoded fliC homologue. This mechanism potentially enables bacteria to evade immune responses and alter motility.

This research uncovers a new evolutionary path of transposon-derived, RNA-guided nucleases and accentuates the molecular opportunities permitted by transposon gene exaptation. The study provides insights into bacterial adaptation mechanisms and potential new tools for genome engineering.

An IonOpticks Aurora Ultimate CSI 25×75 C18 UHPLC column was used for high-resolution peptide separation in the liquid chromatography with tandem mass spectrometry experiments, enabling detailed proteomic analysis of flagellar samples.

Publication
Nature

Authors

Tanner Wiegand, Florian T. Hoffmann, Matt W. G. Walker, Stephen Tang, Egill Richard, Hoang C. Le, Chance Meers & Samuel H. Sternberg

Title

TnpB homologues exapted from transposons are RNA-guided transcription factors