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Mol. Cell. Biol., Feb 1997, 999-1009, Vol 17, No. 2
CM Hart, K Zhao and UK Laemmli
Boundary elements are thought to define the peripheries of chromatin
domains and to restrict enhancer-promoter interactions to their target
genes within their domains. We previously characterized a cDNA encoding the
BEAF-32A protein (32A), which binds with high affinity to the scs' boundary
element from the Drosophila melanogaster 87A7 hsp70 locus. Here, we report
a second protein, BEAF-32B, that differs from 32A only in its amino
terminus. Unlike 32A, it has the same DNA binding specificity as the
complete BEAF activity affinity purified from Drosophila. We characterize
three domains in these proteins. Heterocomplex formation is mediated by
their identical carboxy-terminal domains, and DNA binding is mediated by
their unique amino-terminal domains. The identical middle domains of 32A
and 32B are dispensable for the functions described here, although they may
be important for boundary element function. 32A and 32B apparently form
trimers, and the ratio of 32A to 32B varies at different loci on polytene
chromosomes as judged by immunofluorescence. The scs' element contains a
high- and low- affinity binding site for BEAF. We observed that interaction
with the low-affinity site is facilitated by binding to the high-affinity
site some 200 bp distant.
Copyright © 1997, American Society for Microbiology
The scs' boundary element: characterization of boundary element- associated factors
Department of Biochemistry, University of Geneva, Switzerland.
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