J Biol Chem, Vol. 273, Issue 16, 9790-9796, April 17, 1998
Analysis of the DNA-binding Site for Xenopus
Glucocorticoid Receptor Accessory Factor
CRITICAL NUCLEOTIDES FOR BINDING SPECIFICITY IN VITRO
AND FOR AMPLIFICATION OF STEROID-INDUCED FIBRINOGEN GENE
TRANSCRIPTION
Min
Li,
Xiongwen
Ye,
Robert N.
Woodward,
Cindy
Zhu,
LaNita A.
Nichols, and
Lené J.
Holland
From the Department of Physiology, University of Missouri School of
Medicine, Columbia, Missouri 65212
In addition to the glucocorticoid receptor,
DNA-binding proteins called accessory factors play a role in hormone
activation of many glucocorticoid-responsive genes. Hormonal regulation
of the
-fibrinogen subunit gene from the frog Xenopus
laevis requires a novel DNA sequence that binds a liver nuclear
protein called Xenopus glucocorticoid receptor accessory
factor (XGRAF). Here we demonstrate that the recognition site for XGRAF
encompasses GAGTTAA at positions
175 to
169 relative to the start
site of transcription. This sequence is not closely related to the
binding sites for known transcription factors. The two guanosines make close contact with XGRAF, as shown by the methylation interference assay. Single-point mutagenesis of every nucleotide in the 9-base pair
region from positions
177 to
169 showed an excellent correlation between ability to bind XGRAF in vitro and ability to
amplify hormone-induced transcription from DNA transfected into
Xenopus primary hepatocytes. Conversely, XGRAF had little
or no effect on basal transcription of the
-fibrinogen gene. Maximal
hormonal induction also requires three half-glucocorticoid response
elements (half-GREs) homologous to the downstream half of the consensus GRE. Interestingly, the XGRAF-binding site is immediately adjacent to
the most important half-GRE. This close proximity suggests a new
mechanism for activation of a gene lacking a conventional full GRE.
Copyright © 1998 by The American Society for Biochemistry and Molecular Biology, Inc.