title: Deconvoluting the structural and drug-recognition complexity of the G-quadruplex-forming region upstream of the bcl-2 P1 promoter.
abstract: The human bcl-2 gene contains a GC-rich region upstream of the P1 promoter that has been shown to be critically involved in the regulation of bcl-2 gene expression. We have demonstrated that the guanine-rich strand of the DNA in this region can form any one of three distinct intramolecular G-quadruplex structures. Mutation and deletion analysis permitted isolation and identification of three overlapping DNA sequences within this element that formed the three individual G-quadruplexes. Each of these was characterized using nondenaturing gel analysis, DMS footprinting, and circular dichroism. The central G-quadruplex, which is the most stable, forms a mixed parallel/antiparallel structure consisting of three tetrads connected by loops of one, seven, and three bases. Three different G-quadruplex-interactive agents were found to further stabilize these structures, with individual selectivity toward one or more of these G-quadruplexes. Collectively, these results suggest that the multiple G-quadruplexes identified in the promoter region of the bcl-2 gene are likely to play a similar role to the G-quadruplexes in the c-myc promoter in that their formation could serve to modulate gene transcription. Last, we demonstrate that the complexity of the G-quadruplexes in the bcl-2 promoter extends beyond the ability to form any one of three separate G-quadruplexes to each having the capacity to form either three or six different loop isomers. These results are discussed in relation to the biological significance of this G-quadruplex-forming element in modulation of bcl-2 gene expression and the inherent complexity of the system where different G-quadruplexes and loop isomers are possible.
authors.affiliation: College of Pharmacy, University of Arizona, Tucson, Arizona 85721, USA.
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Dexheimer
authors.forename: Daekyu
authors.initials: D
authors.lastname: Sun
authors.forename: Laurence H
authors.initials: LH
authors.lastname: Hurley
mesh_terms: D001483:Base Sequence; D002942:Circular Dichroism; D004247:DNA / Q000187:drug effects*; D019254:Genes, bcl-2; D011401:Promoter Regions, Genetic
chemical_list: D004247:DNA