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(Received for publication, March 7, 1997, and in revised form, June 25, 1997)
From the Department of Pharmacology and Toxicology and the Massey
Cancer Center, Medical College of Virginia, Virginia Commonwealth
University, Richmond, Virginia 23298
In mammals, folylpoly-
Volume 272, Number 40,
Issue of October 3, 1997
pp. 25373-25379
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.
-glutamate
Synthetase Gene
-glutamate synthetase
(FPGS) activity is found in any cell undergoing sustained proliferative
phases, but this enzyme also displays a tissue-specific pattern of
expression in differentiated tissues. It is now reported that the
steady state levels of FPGS mRNA in normal and neoplastic cells
reflect these patterns, supporting the concept that the control
mechanisms underlying this distribution are transcriptional. To
initiate an understanding of these interacting levels of control, we
have determined the position and properties of the minimal FPGS
promoter controlling transcription of the FPGS gene in human CEM
leukemia cells, a line which expresses high levels of this enzyme and
its mRNA. The TATA-less region immediately upstream of the major
transcriptional start site previously mapped in human tumor cells,
which includes several GC- and Y-boxes, functioned as a remarkably
efficient promoter when used to drive expression of a luciferase
reporter in transient expression studies in CEM cells. The minimal
region of the FPGS promoter required for maximal transcriptional
activation in CEM cells included the 80 base pairs over which the
multiple transcriptional start sites were located, and the 43 base
pairs immediately upstream. DNase I footprint analysis detected the binding of Sp1 at all seven of the consensus sites within the probe
used, two of which are contained within the minimal promoter region.
The several Sp1 sites immediately upstream of the first major
transcriptional start activated transcription in Drosophila cells when cotransfected with an Sp1 construct, including those in the
region which functioned as a minimal promoter in CEM cells. An
additional region of the minimal promoter, situated between the two
translational start codons of the FPGS gene, was bound by protein(s)
from HeLa cell nuclear extracts. We conclude that transcription of the
FPGS gene in CEM cells involves transactivation events over a limited
upstream DNA sequence and that the FPGS promoter used in proliferating
human leukemic cells has strong similarity to other TATA-less promoters
that utilize tandem, closely spaced Sp1 sites to initiate
transcription.
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