Published online 8 December 2004
Nucleic Acids Research, Vol. 32 No. 21 © Oxford University Press 2004; all rights reserved
Synthesis of unimolecularly circular G-quadruplexes as prospective molecular probes
1 Department of Pharmaceutics, School of Pharmacy, 2 National Research Laboratories of Natural and Biomimetic Drugs, Peking University, 38 Xueyuan Road, Hiandian District, Beijing 100083, The People's Republic of China, 3 Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong and 4 Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543
* To whom correspondence should be addressed. Tel: +65 68747961; Fax: +65 67791691; Email: chmlth{at}nus.edu.sg
Correspondence may also be addressed to Ming Yang, Tel: +86 1082801569; Fax: +86 1082 802062; Email: yangm{at}bjmu.edu.cn and Qiang Zhang, Tel: +86 1082 802781; Fax: +86 1082 802791; Email: dodozq{at}sohu.com
Received as resubmission August 7, 2004; Revised October 10, 2004; Accepted November 1, 2004
Synthesis of unimolecularly circular G-quadruplex has been accomplished for the first time during our investigation on the template basis of G-quadruplex through chemical ligations of guanine-rich linear sequences of oligodeoxyribonucleotides. The uniqueness of this newly designed circularization course is its self-recognition and self-templating on the scale of individual strand of oligodeoxyribonucleotide in which the same linear sequence serves both as a template and as a substrate simultaneously. The results from our exonuclease and DNAse hydrolysis studies confirm that there is indeed absence of open termini within the structure of the identified circular product. Our subsequent investigation on the loop-size effect indicates that the unimolecularly circular G-quadruplex possessing two or more thymine nucleotides within their connecting loops is readily attainable, while the linear sequence with a single thymine nucleotide between guanine tracts is not a proper precursor for our ligation reaction. In addition, conformation dependency of the circularization course as well as the effects of alkali ions, pH values and concentration of potassium ions on the circularization reaction are examined during our investigation. The implication of our current studies and possible application of the obtained unimolecularly circular G-quadruplex in certain biological processes are also discussed in this report.
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