FIGURE 1.

A, general scheme and rationale of the genetic screen, aimed at isolating intrinsically active (MEK-independent) Mpk1 molecules. The asterisk indicates a Mkk1/Mkk2-independent, intrinsically active Mpk1. B, Mpk1 molecules harboring the point mutations isolated in the screen allow mkk1Δmkk2Δ cells to grow in the presence of 17 mm caffeine. Patches of the indicated strains were allowed to grow on a YNB-URA plate for 48 h and then replica-plated to the plate shown, containing YPD supplemented with 17 mm caffeine. Patches of three different colonies are shown for each mutant. Single patches are shown for controls. All patches grew similarly in the absence of caffeine (data not shown).