A SAM-I riboswitch with the ability to sense and respond to uncharged initiator tRNA

Nat Commun. 2020 Jun 3;11(1):2794. doi: 10.1038/s41467-020-16417-z.

Abstract

All known riboswitches use their aptamer to senese one metabolite signal and their expression platform to regulate gene expression. Here, we characterize a SAM-I riboswitch (SAM-IXcc) from the Xanthomonas campestris that regulates methionine synthesis via the met operon. In vitro and in vivo experiments show that SAM-IXcc controls the met operon primarily at the translational level in response to cellular S-adenosylmethionine (SAM) levels. Biochemical and genetic data demonstrate that SAM-IXcc expression platform not only can repress gene expression in response to SAM binding to SAM-IXcc aptamer but also can sense and bind uncharged initiator Met tRNA, resulting in the sequestering of the anti-Shine-Dalgarno (SD) sequence and freeing the SD for translation initiation. These findings identify a SAM-I riboswitch with a dual functioning expression platform that regulates methionine synthesis through a previously unrecognized mechanism and discover a natural tRNA-sensing RNA element. This SAM-I riboswitch appears to be highly conserved in Xanthomonas species.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Base Sequence
  • Genetic Loci
  • Models, Biological
  • Nucleic Acid Conformation
  • Operon / genetics
  • Protein Biosynthesis
  • RNA, Transfer, Met / chemistry
  • RNA, Transfer, Met / genetics
  • RNA, Transfer, Met / metabolism*
  • Riboswitch*
  • S-Adenosylmethionine / metabolism*

Substances

  • RNA, Transfer, Met
  • Riboswitch
  • S-Adenosylmethionine