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Molecular and Cellular Biology, February 2008, p. 1047-1060, Vol. 28, No. 3
0270-7306/08/$08.00+0 doi:10.1128/MCB.01622-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Julia Manasson,
and
Paul Schedl*
Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544
Received 3 September 2007/ Returned for modification 1 November 2007/ Accepted 12 November 2007
The Fab-7 boundary is required to ensure that the iab-6 and iab-7 cis-regulatory domains in the Drosophila Bithorax complex can function autonomously. Though Fab-7 functions as a boundary from early embryogenesis through to the adult stage, this constitutive boundary activity depends on subelements whose activity is developmentally restricted. In the studies reported here, we have identified a factor, called early boundary activity (Elba), that confers Fab-7 boundary activity during early embryogenesis. The Elba factor binds to a recognition sequence within a Fab-7 subelement that has enhancer-blocking activity during early embryogenesis, but not during mid-embryogenesis or in the adult. We found that the Elba factor is present in early embryos but largely disappears during mid-embryogenesis. We show that mutations in the Elba recognition sequence that eliminate Elba binding in nuclear extracts disrupt the early boundary activity of the Fab-7 subelement. Conversely, we find that early boundary activity can be reconstituted by multimerizing the Elba recognition site.
Published ahead of print on 26 November 2007.
Present address: Chandrika, Biscayne Bay, FL.
Present address: Boston University Medical School, Boston, MA.
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