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Mol. Cell. Biol., May 1997, 2529-2537, Vol 17, No. 5
KE Boyd and PJ Farnham
Carbamoyl-phosphate synthase/aspartate carbamoyltransferase/dihydroorotase,
which is encoded by the cad gene, is required for the first three
rate-limiting steps of de novo pyrimidine biosynthesis. It has been
previously demonstrated that cad transcription increases at the G1/S-phase
boundary, as quiescent cells reenter the proliferative cell cycle. The
growth-responsive element has been mapped to an E box at +65 in the hamster
cad promoter. Using an in vivo UV cross-linking and immunoprecipitation
assay, we show that Myc, Max, and upstream stimulatory factor (USF) bind to
the chromosomal cad promoter. To determine whether binding of Myc-Max or
USF is critical for cad growth regulation, we analyzed promoter constructs
which contain mutations in the nucleotides flanking the E box. We
demonstrate that altering nucleotides which flank the cad E box to
sequences which decrease Myc-Max binding in vitro correlates with a loss of
cad G1/S- phase transcriptional activation. This result supports the
conclusion that binding of Myc-Max, but not USF, is essential for cad
regulation. Our investigations demonstrate that the endogenous cad E box
can be bound by more than one transcription factor, but growth-induced cad
expression is achieved only by Myc.
Copyright © 1997, American Society for Microbiology
Myc versus USF: discrimination at the cad gene is determined by core promoter elements
McArdle Laboratory for Cancer Research, University of Wisconsin Medical School, Madison 53706, USA.
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