FIG. 5.

The EYA-SO transcription factor is regulated by phosphorylation. (A) As shown in Fig. 3, the EYA-SO transcription factor can activate expression of ARE-luciferase. This expression is not affected by addition of RAS^V12 nor upon mutation of the MAPK phosphoacceptor sites to alanine (EYA^S-A). A striking increase in activation is seen when the EYA^S-D/E phosphomimetic mutant is used, showing that phosphorylation acts to increase EYA transactivation potential. That RAS^V12 itself does not produce the same increase on wild-type EYA (WT) in this assay suggests that RAS signaling may have multiple effects on the RD gene network and in particular may negatively regulate SO. (B) EYA phosphoacceptor mutations do not affect protein expression levels.