Chromatin structure of the potential Z-forming sequence (dT-dG)n · (dC-dA)n. Evidence for an "alternating-B" conformation

David S. Gross, Sue Ying Huang, William T. Garrard

Research output: Contribution to journalArticlepeer-review

28 Scopus citations


The sequence (dT-dG)n · (dC-dA)n is the most abundant purine-pyrimidine dinucleotide repeat in eukaryotic genomes. This sequence and certain others that contain alternating purine-pyrimidine residues have been shown to adopt the left-handed, Z-DNA conformation in vitro when subjected to negative torsional stress or elevated ionic strengths. We have asked whether (dT-dG)n · (dC-dA)n tracts exist in topologically constrained Z-form structures in vivo by examining the chromatin organization of these sequences in cultured mouse cell nuclei. We find that these elements are quantitatively packaged into typical core particles which are embedded in canonical polynucleosomal arrays. In addition, these sequences neither flank nor reside within regions of chromatin that are preferentially sensitive to S1 nuclease. These characteristics suggest that these tracts do not exist predominantly in the Z-form in vivo. Furthermore, employing techniques that permit prominent hybridization to DNA fragments as short as 18 bases, we provide evidence that in vivo, most (dT-dG)n · (dC-dA)n elements instead adopt an "alternating-B" conformation on the nucleosomal surface.

Original languageEnglish (US)
Pages (from-to)251-265
Number of pages15
JournalJournal of Molecular Biology
Issue number2
StatePublished - May 25 1985

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology


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