Nucleic Acids Research, Vol 24, Issue 10 1921-1927, Copyright © 1996 by Oxford University Press
SJ Vitola, A Wang and XH Sun
The E2A gene encodes two alternatively spliced products, E12 and E47. The
two proteins differ in their basic helix-loop-helix motifs (bHLH),
responsible for DNA binding and dimerization. Although both E12 and E47 can
bind to DNA as heterodimers with tissue-specific bHLH proteins, E12 binds
to DNA poorly as homodimers. An inhibitory domain in E12 has previously
been found to prevent E12 homodimers from binding to DNA. By measuring the
dissociation rates using filter binding and electrophoretic mobility shift
assays, we have shown here that the inhibitory domain interferes with DNA
binding by destabilizing the DNA- protein complexes. Furthermore, we have
demonstrated that substitution of basic amino acids (not other amino acids)
in the DNA-binding domain of E12 can increase the intrinsic DNA-binding
activity of E12 and stabilize the binding complexes, thus alleviating the
repression from the inhibitory domain. This ability of basic amino acids to
stabilize DNA-binding complexes may be of biological significance in the
case of myogenic bHLH proteins, which all possess two more basic amino
acids in their DNA binding domain than E12. To function as heterodimers
with E12, the myogenic bHLH proteins may need stronger DNA binding domains.
ARTICLES
Substitution of basic amino acids in the basic region stabilizes DNA binding by E12 homodimers
Department of Cell Biology, New York University Medical Center, NY 10016, USA.
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