Mol. Cell. Biol., 09 1995, 5196-5202, Vol 15, No. 9
SK Thukral, Y Lu, GC Blain, TS Harvey and VL Jacobsen
Critical determinants of DNA recognition by p53 have been identified by a
molecular genetic approach. The wild-type human p53 fragment containing
amino acids 71 to 330 (p53(71-330)) was used for in vitro DNA binding
assays, and full-length human p53 was used for transactivation assays with
Saccharomyces cerevisiae. First, we defined the DNA binding specificity of
the wild-type p53 fragment by using systematically altered forms of a known
consensus DNA site. This refinement indicates that p53 binds with high
affinity to two repeats of PuGPuCA.TGPyCPy, a further refinement of an
earlier defined consensus half site PuPuPuC(A/T).(T/A) GPyPyPy. These
results were further confirmed by transactivation assays of yeast by using
full- length human p53 and systematically altered DNA sites. Dimers of the
pentamer AGGCA oriented either head-to-head or tail-to-tail bound
efficiently, but transactivation was facilitated only through head-to- head
dimers. To determine the origins of specificity in DNA binding by p53, we
identified mutations that lead to altered specificities of DNA binding.
Single-amino-acid substitutions were made at several positions within the
DNA binding domain of p53, and this set of p53 point mutants were tested
with DNA site variants for DNA binding. DNA binding analyses showed that
the mutants Lys-120 to Asn, Cys-277 to Gln or Arg, and Arg-283 to Gln bind
to sites with noncanonical base pair changes at positions 2, 3, and 1 in
the pentamer (PuGPuCA), respectively. Thus, we implicate these residues in
amino acid-base pair contacts. Interestingly, mutant Cys-277 to Gln bound a
consensus site as two and four monomers, as opposed to the wild-type p53
fragment, which invariably binds this site as four monomers.
Copyright © 1995, American Society for Microbiology
Discrimination of DNA binding sites by mutant p53 proteins
Department of Developmental Biology, Amgen, Thousand Oaks, California 91320, USA.
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