Sa. Moodie et al., ASSOCIATION OF MEK1 WITH P21(RAS)CENTER-DOT-GMPPNP IS DEPENDENT ON B-RAF, Molecular and cellular biology, 14(11), 1994, pp. 7153-7162
We have previously reported that immobilized p21(ras) forms a GMPPNP-d
ependent complex with a MEK activity. Furthermore, the association of
the MEK activity was found to be independent of the presence of Raf-1.
We have extended those observations to show that MEK1 is the MEK acti
vity previously described to associate with immobilized p21(ras) . GMP
PNP. The association between MEK1 and immobilized p21(ras) . GMPPNP in
creased its specific activity towards p42(MAPK). We detected the speci
fic association of B-Raf with immobilized p21(ras) . GMPPNP. In contra
st to Raf-1-immunodepleted lysates, preclearance of the cytosolic B-Ra
f significantly reduced, by 96%, the amount of MEK1 activity associate
d with immobilized p21(ras) . GMPPNP. The decrease in MEK1 activity co
rrelated with complete loss in the binding of both B-Raf and MEK1 prot
eins with immobilized p21(ras) . GMPPNP. These data suggest that the p
21(ras) . GMPPNP-dependent activation of MEK1 in brain extracts is dep
endent on the presence of the B-Raf protein kinase.