UASt regulates expression of rl containing a serine instead of an arginine at position amino acid 80 as well as the "sevenmaker" gain-of-function mutation (D334N). The R68S mutation was initially identified in the yeast ERK, Mpk1, and renders Mpk1 intrinsically active; mutations at the equivalent residue of human ERK1 (R84) and ERK2 (R65) have been found in human tumors. The equivalent mutation to D334N is found in cancer patients (D321N in human ERK2).