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Mol. Cell. Biol., 01 1998, 102-109, Vol 18, No. 1
H Asano and G Stamatoyannopoulos
Erythroid Kruppel-like factor (EKLF), an erythroid tissue-specific
Kruppel-type zinc finger protein, binds to the beta-globin gene CACCC box
and is essential for beta-globin gene expression. EKLF does not activate
the gamma gene, the CACCC sequence of which differs from that of the beta
gene. To test whether the CACCC box sequence difference is the primary
determinant of the selective activation of the beta gene by EKLF, the CACCC
boxes of beta and gamma genes were swapped and the resulting promoter
activities were assayed by transient transfections in CV-1 cells. EKLF
activated the beta promoter carrying a gamma CACCC box at a level
comparable to that at which it activated the wild-type beta promoter,
whereas EKLF failed to activate a gamma promoter carrying the beta CACCC
box, despite the presence of the optimal EKLF binding site. Similar results
were obtained in K562 cells. The possibility that overexpressed EKLF
superactivated the beta promoter carrying the gamma CACCC box, or that EKLF
activated the mutated beta promoter through the intact distal CACCC box,
was excluded. To test whether the position of the CACCC box in the beta or
gamma promoter determined EKLF specificity, the proximal beta CACCC box
sequence was created at the position of the beta promoter (-140) which
corresponds to the position of the CACCC box on the gamma promoter.
Similarly, the beta CACCC box was created in the position of the gamma
promoter (-90) corresponding to the position of the CACCC box in the beta
promoter. EKLF retained weak activation potential on the beta(-140CAC)
promoter, whereas EKLF failed to activate the gamma(-90betaCAC) promoter
even though that promoter contained an optimal EKLF binding site at the
optimal position. Taken together, our findings indicate that the
specificity of the activation of the beta promoter by EKLF is determined by
the overall structure of the beta promoter rather than solely by the
sequence of the beta gene CACCC box.
Copyright © 1998, American Society for Microbiology
Activation of beta-globin promoter by erythroid Kruppel-like factor
Division of Medical Genetics, University of Washington, Seattle 98195, USA.
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