Nucleic Acids Research, Vol 27, Issue 7 1740-1746, Copyright © 1999 by Oxford University Press
MA Bounpheng, IN Melnikova, JJ Dimas and BA Christy
The Id proteins are a family of related mammalian helix-loop-helix (HLH)
proteins which can interact with other HLH proteins but lack a basic region
and are thus not thought to bind to DNA. Instead, they are hypothesized to
act as dominant negative regulators of DNA-binding basic HLH (bHLH)
proteins, by forming inactive heterodimers with these proteins. All four Id
family proteins possess related HLH dimerization domains and can interact
with similar bHLH proteins, although with differing affinities. The
functions of the largely unrelated N- and C- terminal regions of the
proteins are unknown. In this study, we have identified a novel
transcriptional activity of the mammalian Id proteins. We show that when
fused to the heterologous GAL4 DNA-binding domain, all four of the
mammalian Id proteins can activate GAL4- dependent transcription. The HLH
domain is necessary for the transactivation activity observed, suggesting
that interaction with a cellular HLH protein is required. Co-transfection
with exogenous Class A bHLH proteins (E-proteins) greatly potentiates the
transactivation, which is abolished upon co-transfection with Class B bHLH
proteins. These results are consistent with the idea that the Id proteins
have a transcriptional activity when present in a DNA-binding complex.
ARTICLES
Identification of a novel transcriptional activity of mammalian Id proteins
Department of Cellular and Structural Biology, Institute of Biotechnology, University of Texas Health Science Center, San Antonio, TX 78245-3207, USA.
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