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Molecular and Cellular Biology, March 2003, p. 1737-1749, Vol. 23, No. 5
0270-7306/03/$08.00+0     DOI: 10.1128/MCB.23.5.1737-1749.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Asymmetric Recognition of Nonconsensus AP-1 Sites by Fos-Jun and Jun-Jun Influences Transcriptional Cooperativity with NFAT1

Vladimir Ramirez-Carrozzi{dagger} and Tom Kerppola*

Howard Hughes Medical Institute and Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan 48109-0650,

Received 28 August 2002/ Returned for modification 18 October 2002/ Accepted 26 November 2002

Many regulatory elements in eukaryotic promoters do not correspond to optimal recognition sequences for the transcription factors that regulate promoter function by binding to the elements. The sequence of the binding site may influence the structural and functional properties of regulatory protein complexes. Fos-Jun heterodimers were found to bind nonconsensus AP-1 sites in a preferred orientation. Oriented Fos-Jun heterodimer binding was attributed to nonidentical recognition of the two half-sites by Fos and Jun. Jun bound preferentially to the consensus half-site, whereas Fos was able to bind nonconsensus half-sites. The orientation of heterodimer binding affected the transcriptional cooperativity of Fos-Jun-NFAT1 complexes at composite regulatory elements in mammalian cells. Jun dimerization with Fos versus ATF2 caused it to bind opposite half-sites at nonconsensus AP-1 elements. Similarly, ATF2 bound to opposite half-sites in Fos-ATF2-NFAT1 and ATF2-Jun-NFAT1 complexes. The orientations of nonconsensus AP-1 sites within composite regulatory elements affected the cooperativity of Fos-Jun as well as Jun-Jun binding with NFAT1. Since Jun homodimers cannot bind to AP-1 sites in a preferred orientation, the effects of the orientations of nonconsensus AP-1 sites on the stabilities of Jun-Jun-NFAT1 complexes are likely to be due to asymmetric conformational changes in the two subunits of the homodimer. Nonconsensus AP-1 site orientation also affected the synergy of transcription activation between Jun homodimers and NFAT1 at composite regulatory elements. The asymmetric recognition of nonconsensus AP-1 sites can therefore influence the transcriptional activities of Fos and Jun both through effects on the orientation of heterodimer binding and through differential conformational changes in the two subunits of the dimer.


* Corresponding author. Mailing address: Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, MI 48109-0650. Phone: (734) 615-1703. Fax: (734) 615-3397. E-mail: kerppola{at}umich.edu.

{dagger} Present address: Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, CA 90095-1662.


Molecular and Cellular Biology, March 2003, p. 1737-1749, Vol. 23, No. 5
0022-538X/03/$08.00+0     DOI: 10.1128/MCB.23.5.1737-1749.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.




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