J Biol Chem, Vol. 274, Issue 36, 25419-25425, September 3, 1999
Mutations That Increase Acidity Enhance the Transcriptional
Activity of the Glutamine-rich Activation Domain in Stage-specific
Activator Protein
Mitchel L.
Benuck,
Zhe
Li, and
Geoffrey
Childs
From the Department of Molecular Genetics, Albert Einstein College
of Medicine, Bronx, New York 10461
Sea urchin stage-specific activator protein
(SSAP) activates transcription of the late H1 gene at the mid-blastula
stage of development. Its C-terminal 202 amino acids form a potent
glycine/glutamine rich activation domain (GQ domain) that can
transactivate reporter genes to levels 5-fold higher than VP16 in
several mammalian cell lines. We observed that, unlike other
glutamine-rich activation domains, the GQ domain activates
transcription to moderate levels in yeast. We utilized this activity to
screen in yeast for intragenic mutations that enhance or inhibit the
transcriptional activity of the GQ domain. We identified 37 loss of
function and 23 gain of function mutants. Most gain of function
mutations increased the acidity of the domain. The most frequently
isolated mutations conferred enhanced transcriptional activity when
assayed in mammalian cells. These mutations also enhance the ability of
SSAP to up-regulate the late H1 promoter in sea urchin embryos. We
conclude that the GQ domain fundamentally differs from other
glutamine-rich activators and may share some properties of acidic
activators. The ability of acidity to enhance SSAP-mediated
transcription may reflect a mechanism by which phosphorylation of SSAP
activates late H1 gene transcription during embryogenesis.
Copyright © 1999 by The American Society for Biochemistry and Molecular Biology, Inc.