title: Solution equilibria of the i-motif-forming region upstream of the B-cell lymphoma-2 P1 promoter.
abstract: The 5'-end of the P1 promoter of the B-cell lymphoma-2 (bcl-2) gene contains a highly guaninecytosine-rich region, which has a role in the regulation of bcl-2 transcription. Whereas the guanine-rich region has been the focus of recent studies, little attention has been paid to the cytosine-rich strand. Here we examine the structural transitions of the cytosine-rich sequence by means of acid-base, mole-ratio and melting experiments monitored by molecular absorption, circular dichroism, and NMR spectroscopies. Two intramolecular i-motif structures have been detected in the pH range 2-7, with maximal formation at pH 4 and 6, respectively. At pH 7.6 the majority species has been associated with a hairpin involving Watson-Crick base pairs. Upon addition of the quadruplex-interacting ligand TmPyP4, bcl-2c structures at pH 6.1 and 7.6 yield identical interaction species with stoichiometries 1:2 (DNA:ligand) and logarithms of formation constant 12.4+/-0.2 and 11.7+/-0.1, respectively. The initial i-motif structure at pH 6.1 is lost upon interaction with TmPyP4.
authors.affiliation: Department of Analytical Chemistry, University of Barcelona, Diagonal 647, E-08028 Barcelona, Spain.
authors.forename: Nasiruddin
authors.initials: N
authors.lastname: Khan
authors.forename: Anna
authors.initials: A
authors.lastname: Aviñó
authors.forename: Romà
authors.initials: R
authors.lastname: Tauler
authors.forename: Carlos
authors.initials: C
authors.lastname: González
authors.forename: Ramon
authors.initials: R
authors.lastname: Eritja
authors.forename: Raimundo
authors.initials: R
authors.lastname: Gargallo
mesh_terms: D020816:Amino Acid Motifs; D001483:Base Sequence; D002942:Circular Dichroism; D003596:Cytosine / Q000737:chemistry; D004247:DNA / Q000737:chemistry* / Q000235:genetics; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D016393:Lymphoma, B-Cell / Q000235:genetics* / Q000473:pathology; D008956:Models, Chemical; D019906:Nuclear Magnetic Resonance, Biomolecular; D011166:Porphyrins / Q000737:chemistry; D011401:Promoter Regions, Genetic; D012996:Solutions; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature; D013816:Thermodynamics
chemical_list: D008024:Ligands; D011166:Porphyrins; D012996:Solutions; D003596:Cytosine; D004247:DNA