A novel G•G•T non-conventional intramolecular triplex formed by the double repeat sequence of Chlamydomonas telomeric DNA

Competition among DNA non-canonical structures has been widely studied in repetitive DNA sequences. The factors affecting DNA structural polymorphism have always been an important area of research. The Chlamydomonas reinhardtii telomere (TTTTAGGG)(n) is found to be an exception to the general idea of forming a folded G-quadruplex by a few repeats in any telomeric sequence. Herein, using gel electrophoresis, UV thermal melting, UV thermal difference spectra (TDS), circular dichroism, and fluorescence and NMR spectroscopy. We demonstrated that the double repeat of the C. reinhardtii telomere (TTTTAGGG)(2) (Chlm2) adopts an intramolecular non-conventional triplex structure in Na+ solution. We report that the co-existence of reverse Hoogsteen (G center dot G) and Wobble base pairing (G center dot T) stabilizes the triplex structure. To the best of our knowledge, such a non-conventional triplex structure formed by any telomeric sequence has not been reported to date.

Automated summary

This study reveals the formation of an intramolecular non-conventional triplex structure by Chlamydomonas reinhardtii telomere in Na+ solution, which is stabilized by the co-existence of reverse Hoogsteen and Wobble base pairing.