| Autor: |
Wiegand T; Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, USA., Hoffmann FT; Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, USA., Walker MWG; Department of Biological Sciences, Columbia University, New York, NY, USA., Tang S; Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, USA., Richard E; Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, USA., Le HC; Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, USA., Meers C; Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, USA., Sternberg SH; Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, USA. |
| Abstrakt: |
Transposon-encoded tnpB genes encode RNA-guided DNA nucleases that promote their own selfish spread through targeted DNA cleavage and homologous recombination 1-4 . This widespread gene family was repeatedly domesticated over evolutionary timescales, leading to the emergence of diverse CRISPR-associated nucleases including Cas9 and Cas12 5,6 . We set out to test the hypothesis that TnpB nucleases may have also been repurposed for novel, unexpected functions other than CRISPR-Cas. Here, using phylogenetics, structural predictions, comparative genomics, and functional assays, we uncover multiple instances of programmable transcription factors that we name TnpB-like nuclease-dead repressors (TldR). These proteins employ naturally occurring guide RNAs to specifically target conserved promoter regions of the genome, leading to potent gene repression in a mechanism akin to CRISPRi technologies invented by humans 7 . Focusing on a TldR clade found broadly in Enterobacteriaceae , we discover that bacteriophages exploit the combined action of TldR and an adjacently encoded phage gene to alter the expression and composition of the host flagellar assembly, a transformation with the potential to impact motility 8 , phage susceptibility 9 , and host immunity 10 . Collectively, this work showcases the diverse molecular innovations that were enabled through repeated exaptation of genes encoded by transposable elements, and reveals that RNA-guided transcription factors emerged long before the development of dCas9-based editors. |
