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Molecular and Cellular Biology, February 2007, p. 963-974, Vol. 27, No. 3
0270-7306/07/$08.00+0     doi:10.1128/MCB.00795-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Integrity of the Mod(mdg4)-67.2 BTB Domain Is Critical to Insulator Function in Drosophila melanogaster ^,

Institute of Gene Biology, Russian Academy of Sciences, Moscow 119334, Russia,¹ University of Oslo, Centre for Medical Studies in Russia, Moscow 119334, Russia,² Institute of Molecular Biology, Moscow 119334, Russia,³ Department of Biochemistry, University of Iowa, Iowa City, Iowa 52242,⁴ Department of Biological Sciences, University of Dundee, Dundee DD1 4HN, Scotland, United Kingdom,⁵ Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, New Jersey 08854⁶

Received 5 May 2006/ Returned for modification 31 July 2006/ Accepted 30 October 2006

The Drosophila gypsy insulator contains binding sites for the Suppressor of Hairy-wing [Su(Hw)] protein. Enhancer and silencer blocking require Su(Hw) recruitment of Mod(mdg4)-67.2, a BTB/POZ domain protein that interacts with Su(Hw) through a carboxyl-terminal acidic domain. Here we conducted mutational analyses of the Mod(mdg4)-67.2 BTB domain. We demonstrate that this domain is essential for insulator function, in part through direction of protein dimerization. Our studies revealed the presence of a second domain (DD) that contributes to Mod(mdg4)-67.2 dimerization when the function of the BTB domain is compromised. Additionally, we demonstrate that mutations in amino acids of the charged pocket in the BTB domain that retain dimerization of the mutated protein cause a loss of insulator function. In these cases, the mutant proteins failed to localize to chromosomes, suggesting a role for the BTB domain in chromosome association. Interestingly, replacement of the Mod(mdg4)-67.2 BTB domain with the GAF BTB domain produced a nonfunctional protein. Taken together, these data suggest that the Mod(mdg4)-67.2 BTB domain confers novel activities to gypsy insulator function.

Published ahead of print on 13 November 2006.

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