title: Methylation of the Z-DNA decamer d(GC)5 potentiates the formation of A-DNA: crystal structure of d(Gm5CGm5CGCGCGC).
abstract: It is well known that methylation of alternating Py x Pu sequences potentiates the formation of Z-DNA. However, we have now observed that methylation of the alternating Z-DNA oligomer d(GCGCGCGCGC), which starts with a 5'-purine, unexpectedly stabilizes the A-DNA conformation. The double methyl derivative d(Gm5CGm5CGCGCGC), which crystallizes as duplex A-DNA in the hexagonal space group P6(1)22, a = b = 39.33 A and c = 77.93 A with one strand per asymmetric unit and six duplexes in the unit cell, refined to an R factor of 19.1 for 204 DNA atoms and 43 solvent molecules. This is the first report of a DNA sequence crystallized in both right and left-handed conformations, allowing structural comparisons not previously possible and, more importantly, this is the first time that methylation has been shown to potentiate the formation of A-DNA from a sequence known to crystallize as Z-DNA. From this study, ten base-pairs appear to be the critical length in determining the handedness of d(GC)n-type sequences in the crystalline state. Because methylation of nuclear DNA is linked to a number of cellular processes, including transcriptional inactivation, this study has important implications for the role of A-DNA in methylated regions of genomic DNA and, thus, in the regulation of gene expression. In this context, the structure of d(Gm5Cm5CGCGCGC) will be compared with that of the alternating A-DNA decamer d(GCACGCGTGC) and the alternating Z-DNA decamer d(GCGCGCGCGC) and discussed in terms of the forces that govern the handedness of duplex DNA oligomers.
authors.affiliation: Biological Macromolecular Structure Center, Department of Chemistry and Biochemistry, The Ohio State University, Columbus 43210-1002, USA.
authors.forename: D B
authors.initials: DB
authors.lastname: Tippin
authors.forename: B
authors.initials: B
authors.lastname: Ramakrishnan
authors.forename: M
authors.initials: M
authors.lastname: Sundaralingam
mesh_terms: D001482:Base Composition; D018899:CpG Islands; D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry* / Q000378:metabolism*; D019175:DNA Methylation; D015226:Dinucleoside Phosphates / Q000737:chemistry; D009690:Nucleic Acid Conformation; D009692:Nucleic Acid Heteroduplexes / Q000737:chemistry / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: D015226:Dinucleoside Phosphates; D009692:Nucleic Acid Heteroduplexes; C054544:2'-deoxyguanylyl-(3'-5')-2'-deoxycytidine; D004247:DNA