Genomic mapping of phosphorothioates reveals partial modification of short consensus sequences

Nat Commun. 2014 Jun 5;5:3951. doi: 10.1038/ncomms4951.


Bacterial phosphorothioate (PT) DNA modifications are incorporated by Dnd proteins A-E and often function with DndF-H as a restriction-modification (R-M) system, as in Escherichia coli B7A. However, bacteria such as Vibrio cyclitrophicus FF75 lack dndF-H, which points to other PT functions. Here we report two novel, orthogonal technologies to map PTs across the genomes of B7A and FF75 with >90% agreement: single molecule, real-time sequencing and deep sequencing of iodine-induced cleavage at PT (ICDS). In B7A, we detect PT on both strands of GpsAAC/GpsTTC motifs, but with only 12% of 40,701 possible sites modified. In contrast, PT in FF75 occurs as a single-strand modification at CpsCA, again with only 14% of 160,541 sites modified. Single-molecule analysis indicates that modification could be partial at any particular genomic site even with active restriction by DndF-H, with direct interaction of modification proteins with GAAC/GTTC sites demonstrated with oligonucleotides. These results point to highly unusual target selection by PT-modification proteins and rule out known R-M mechanisms.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Chromosome Mapping
  • Consensus Sequence / genetics*
  • DNA Restriction-Modification Enzymes
  • DNA, Bacterial / genetics*
  • DNA, Bacterial / metabolism
  • Escherichia coli / genetics*
  • Escherichia coli / metabolism
  • Genome, Bacterial*
  • Phosphates / metabolism*
  • Vibrio / genetics*
  • Vibrio / metabolism


  • DNA Restriction-Modification Enzymes
  • DNA, Bacterial
  • Phosphates
  • thiophosphoric acid