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J. Biol. Chem., Vol. 277, Issue 15, 12937-12945, April 12, 2002
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,
From the Cancer Biology Research Group and Department of
Microbiology and Infectious Diseases, University of Calgary Health
Sciences Centre, Calgary, Alberta, Canada, T2N 4N1
Precisely how mutant p53 exerts a dominant
negative effect over wild type p53 has been an enigma. To understand
how wild type and mutant p53 form hetero-oligomers, we studied p53
biogenesis in vitro. We show here that p53 dimers are
formed cotranslationally (on the polysome), whereas tetramers are
formed posttranslationally (by the dimerization of dimers in solution).
Coexpression of wild type and mutant p53 therefore results in 50% of
the p53 generated being heterotetramers comprised of a
single species: wild type dimer/mutant dimer. Using hot spot
mutants of p53 and a variety of natural target sites, we show
that all wild type/mutant heterotetramers manifest impaired DNA binding
activity. This impairment is not due to the mutant dimeric subunit
inhibiting association of the complex with DNA but rather due to the
lack of significant contribution (positive cooperativity) from the
mutant partner. For all heterotetramers, bias in binding is
particularly pronounced against those sequences in genes responsible
for apoptosis rather than cell growth arrest. These results explain the
molecular basis of p53 dominant negative effect and suggest a
functional role in the regulation of p53 tetramerization.
Recipient of studentships from the National Sciences and
Engineering Research Council and Alberta Heritage Foundation for Medical Research.
§
Present address: Dept. of Hematology and Oncology, St. Jude
Children's Research Hospital, Memphis, TN 38105.
¶
To whom correspondence should be addressed. Tel.:
403-220-7548; Fax: 403-270-8520; E-mail: plee@ucalgary.ca.
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