title: Incorporation of CC steps into Z-DNA: interplay between B-Z junction and Z-DNA helical formation.
abstract: The left-handed DNA structure, Z-DNA, is believed to play important roles in gene expression and regulation. Z-DNA forms sequence-specifically with a preference for sequences rich in pyrimidine/purine dinucleotide steps. In vivo, Z-DNA is generated in the presence of negative supercoiling or upon binding proteins that absorb the high energetic cost of the B-to-Z transition, including the creation of distorted junctions between B-DNA and Z-DNA. To date, the sequence preferences for the B-to-Z transition have primarily been studied in the context of sequence repeats lacking B-Z junctions. Here, we develop a method for characterizing sequence-specific preferences for Z-DNA formation and B-Z junction localization within heterogeneous DNA duplexes that is based on combining 2-aminopurine fluorescence measurements with a new quantitative application of circular dichroism spectroscopy for determining the fraction of B- versus Z-DNA. Using this approach, we show that at least three consecutive CC dinucleotide steps, traditionally thought to disfavor Z-DNA, can be incorporated within heterogeneous Z-DNA containing B-Z junctions upon binding to the Zα domain of the RNA adenosine deaminase protein. Our results indicate that the incorporation of CC steps into Z-DNA is driven by favorable sequence-specific Z-Z and B-Z stacking interactions as well as by sequence-specific energetics that localize the distorted B-Z junction at flexible sites. Together, our results expose higher-order complexities in the Z-DNA code within heterogeneous sequences and suggest that Z-DNA can in principle propagate into a wider range of genomic sequence elements than previously thought.
authors.affiliation: Department of Chemistry and Biophysics, University of Michigan, Ann Arbor, MI 48109, USA.
authors.forename: Jameson R
authors.initials: JR
authors.lastname: Bothe
authors.forename: Ky
authors.initials: K
authors.lastname: Lowenhaupt
authors.forename: Hashim M
authors.initials: HM
authors.lastname: Al-Hashimi
mesh_terms: D000243:Adenosine Deaminase / Q000737:chemistry / Q000378:metabolism; D001483:Base Sequence; D002942:Circular Dichroism; D003596:Cytosine / Q000737:chemistry*; D059371:DNA, B-Form / Q000737:chemistry* / Q000235:genetics; D043542:DNA, Z-Form / Q000737:chemistry* / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation
chemical_list: D059371:DNA, B-Form; D043542:DNA, Z-Form; D003596:Cytosine; D000243:Adenosine Deaminase