Diethyl pyrocarbonate: a chemical probe for secondary structure in negatively supercoiled DNA

Proc Natl Acad Sci U S A. 1985 Dec;82(23):8009-13. doi: 10.1073/pnas.82.23.8009.


Purine residues located within regions of DNA that have the potential to form left-handed Z-helical structures are modified preferentially by diethyl pyrocarbonate; this hyperreactivity is dependent on the degree of negative superhelicity of the circular DNA molecules. As negative superhelical density increases, guanosines in a 32-base-pair alternating G-C sequence and adenosines (but not guanosines) in a 64-base-pair alternating A-C/G-T sequence become 5- to 10-fold more reactive to diethyl pyrocarbonate. The negative superhelical densities at which enhanced reactivity occurs are similar to those reported for the point at which left-handed helices form within plasmids carrying these DNA sequences. Probing of negatively supercoiled pBR322 with diethyl pyrocarbonate reveals a hyperreactive region 31 base pairs in length of which only 9 base pairs are a perfect alternating purine and pyrimidine sequence; the reactivity of purines within this sequence indicates that purines in the anti conformation, or guanosines in the syn conformation with neighboring 3' thymidines, are not hyperreactive in the Z-DNA form.

Publication types

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

MeSH terms

  • Adenosine
  • Alkylation
  • Base Sequence
  • DNA*
  • DNA, Superhelical*
  • Diethyl Pyrocarbonate*
  • Formates*
  • Guanosine
  • Nucleic Acid Conformation*
  • Purines
  • Structure-Activity Relationship


  • DNA, Superhelical
  • Formates
  • Purines
  • Guanosine
  • DNA
  • Adenosine
  • Diethyl Pyrocarbonate