Telomeric dG(GT)4 G Sequence can Adopt Parallel-Stranded Double Helical Conformation
Oligonucleotides 3?-d(GTGTGTGTGG)-L-d(GGTGTGTGTG)-3? (GTL) and 3?-d(G4STG4STG4STG4STGG)-L-d(GGTGTGTGTG)-3? (SGTL), (L=(CH2CH2O)3), were shown by use of several optical techniques to form a novel parallel-stranded (ps) intramolecular double helix with the purine-purine and pyrimidine-pyrimidine base pairing. Rotational relaxation time of the GTL was determined to be similar to that for a 10-bp duplex and a fraction of unpaired bases was derived to be about 7%, testifying to an intramolecular haiprin formation under the experimental conditions. A quasi-two-state mode of the ps double helix formation was validated and the enthalpy -135+5 kJ/mol was acquired. The lifetime of EtBr intercalated in ps dG(GT)4 G hairpin of fluorescence 0.65 of that for EtBr intercalated in antiparallel-stranded (aps) DNA. The schemes of G·G and T·T (4ST ·T) base pairs and conformational parameters of the double helix were derived with molecular modeling by force field techniques. Repetitive d(GT) sequences are abundant in telomeres of different genomes as well as in genes regulatory regions and earlier have been shown to be capable of parallel tetraplex formation (1, 2). The observed conformational potential of the repetitive d(GT) sequence may be of importance for the regulation of cell processes.
1. Borisova, O.F., Shchyolkina, A.K., Timofeev, E.N., Florentiev, V.L. (1992) FEBS Lett. 306, 140-142.
A. K. Shchyolkina, O. F. Borisova, M. A. Livshits, R. Klement1, and T. M. Jovin1
Engelhardt Institute of Molecular Biology,