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Nucleic Acids Research Advance Access first published online on February 5, 2008
This version published online on February 11, 2008
Nucleic Acids Research, doi:10.1093/nar/gkm1069
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© 2007 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Molecular Biology

A novel G-quadruplex-forming GGA repeat region in the c-myb promoter is a critical regulator of promoter activity

SunMi L. Palumbo1, Regan M. Memmott1, Diana J. Uribe1, Yulia Krotova-Khan1, Laurence H. Hurley1,2,3 and Scot W. Ebbinghaus1,*

1Arizona Cancer Center, University of Arizona, 1515 N. Campbell Ave., Tucson, AZ 85724-5024 and 2College of Pharmacy, University of Arizona, 1295 N. Martin Ave., Tucson, AZ 85721, 3BIO5 Institute, University of Arizona, 1657 E. Helen St., Tucson, AZ 85721, USA

*To whom correspondence should be addressed. Tel: +1-267-305-1279; Fax: +267-305-6428; Email: scot_ebbinghaus{at}merck.com

Received May 31, 2007. Revised November 13, 2007. Accepted November 13, 2007.

The c-myb promoter contains multiple GGA repeats beginning 17 bp downstream of the transcription initiation site. GGA repeats have been previously shown to form unusual DNA structures in solution. Results from chemical footprinting, circular dichroism and RNA and DNA polymerase arrest assays on oligonucleotides representing the GGA repeat region of the c-myb promoter demonstrate that the element is able to form tetrad:heptad:heptad:tetrad (T:H:H:T) G-quadruplex structures by stacking two tetrad:heptad G-quadruplexes formed by two of the three (GGA)4 repeats. Deletion of one or two (GGA)4 motifs destabilizes this secondary structure and increases c-myb promoter activity, indicating that the G-quadruplexes formed in the c-myb GGA repeat region may act as a negative regulator of the c-myb promoter. Complete deletion of the c-myb GGA repeat region abolishes c-myb promoter activity, indicating dual roles of the c-myb GGA repeat element as both a transcriptional repressor and an activator. Furthermore, we demonstrated that Myc-associated zinc finger protein (MAZ) represses c-myb promoter activity and binds to the c-myb T:H:H:T G-quadruplexes. Our findings show that the T:H:H:T G-quadruplex-forming region in the c-myb promoter is a critical cis-acting element and may repress c-myb promoter activity through MAZ interaction with G-quadruplexes in the c-myb promoter.


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