Ctional as long as either of the two MAPKKKs is catalytically active. Although less crucial, the MAPKKK heteromer also appears to contribute to prompt activation of the MAPK cascade upon oxidative stress (Supplemental Figure S2; Shiozaki et al., 1998).FIGURE 2: The Wis4 and Win1 MAPKKKs form a heteromer complex. (A) win1:myc and wis4:myc strains were used to monitor the expression levels of the MA