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Molecular and Cellular Biology, October 2001, p. 6598-6605, Vol. 21, No. 19
0270-7306/01/$04.00+0   DOI: 10.1128/MCB.21.19.6598-6605.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

HMG Proteins and DNA Flexibility in Transcription Activation

Eric D. Ross, Philip R. Hardwidge, and L. James Maher III*

Department of Biochemistry and Molecular Biology, Mayo Foundation, Rochester Minnesota 55905

Received 18 April 2001/Returned for modification 31 May 2001/Accepted 27 June 2001

The relative stiffness of naked DNA is evident from measured values of longitudinal persistence length (~150 bp) and torsional persistence length (~180 bp). These parameters predict that certain arrangements of eukaryotic transcription activator proteins in gene promoters should be much more effective than others in fostering protein-protein interactions with the basal RNA polymerase II transcription apparatus. Thus, if such interactions require some kind of DNA looping, DNA loop energies should depend sensitively on helical phasing of protein binding sites, loop size, and intrinsic DNA curvature within the loop. Using families of artificial transcription templates where these parameters were varied, we were surprised to find that the degree of transcription activation by arrays of Gal4-VP1 transcription activators in HeLa cell nuclear extract was sensitive only to the linear distance separating a basal promoter from an array of bound activators on DNA templates. We now examine the hypothesis that this unexpected result is due to factors in the extract that act to enhance apparent DNA flexibility. We demonstrate that HeLa cell nuclear extract is rich in a heat-resistant activity that dramatically enhances apparent DNA longitudinal and torsional flexibility. Recombinant mammalian high-mobility group 2 (HMG-2) protein can substitute for this activity. We propose that the abundance of HMG proteins in eukaryotic nuclei provides an environment in which DNA is made sufficiently flexible to remove many constraints on protein binding site arrangements that would otherwise limit efficient transcription activation to certain promoter geometries.

* Corresponding author. Mailing address: Department of Biochemistry and Molecular Biology, Mayo Foundation, 200 First St., SW, Rochester, MN 55905. Phone: (507) 284-9041. Fax: (507) 284-2053. E-mail: maher{at}mayo.edu.

Molecular and Cellular Biology, October 2001, p. 6598-6605, Vol. 21, No. 19
0270-7306/01/$04.00+0   DOI: 10.1128/MCB.21.19.6598-6605.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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Copyright © 2001 by the American Society for Microbiology. All rights reserved.