FIGURE 6:

Mutating Tyr-280/Tyr-261 in Erk1/2 causes loss-of-function effects on their activity in yeast cells. (A) mpk1Δ or (C) mkk1∆mkk2∆ yeast cells expressing the indicated mammalian Erk2 molecules were plated at five dilutions on plates containing YPD supplemented with 15 mM caffeine (left) or plates without caffeine (YNB(–URA); right). Western blot analysis with the indicated antibodies was performed on protein lysates prepared from (B) mpk1∆ cells or (D) mkk1∆mkk2∆ cells expressing the indicated Erk2 molecules. In B and D, asterisk marks the position of Mpk1 and double asterisks mark the position of Erk2. (E–G) When inserted into a truncated Mpk1 molecule that is very similar to Erk2 (Mpk1Q364), the Y268C and the R68S mutations do not render it intrinsically active but also do not abolish its standard activity.