Sequestered wt p53 fails to bind to its specific
DNA target. (A) EMSA of 5 μg of cytoplasmic extract of
LAN-5 cells, using the p53 CON responsive element without (lane 2) or
with 50-fold excess of specific (lane 3) and various nonspecific (lanes
4–6) competitor DNA. Only a nonspecific band is seen. Lanes 2–6
contain PAb 421 for maximum stimulation of binding. In contrast,
control baculoviral human wt p53 (lanes 12–15) shows a specific band
which supershifts and is greatly enhanced in the presence of PAb 421.
Nuclear extracts of SH DD1-10 cells (lanes 7–9) fail to show a
specific shift, as do nuclear extracts from SaOs 2 p53-null cells
(lanes 10 and 11). Lanes 1–10 and 12–15 are from the same gel. See
text for further details. (B) EMSA of 5 μg of cytoplasmic
extracts of SK-N-SH cells using p53 CON without (lanes 2 and 3) or with
50-fold excess of specific (lane 4) and mutant (lane 5) competitor DNA.
As controls, 5 μg of nuclear ML-1 (lanes 11–15) and LAN-5 extracts
(lanes 21–24) stimulated with actinomycin D show a specific
supershifted band, identical to the one with baculoviral p53. PAb 421
was added as indicated.