A GAL4-cJun, but not a GAL4-Elk1 fusion protein, drives transcription from a reporter construct in PC3 cells in the absence of cotransfected, kinase-expressing plasmids. PathDetect (Stratagene) GAL4-cJun– and GAL4-Elk1–expressing constructs were cotransfected in PC3 cells with plasmids expressing the wild-type or mutant forms of various kinases and with a luciferase reporter plasmid containing 5 GAL4 binding sites (PathDetect; Stratgene). The Jun-driven construct (A) shows high levels of expression in PC3 cells, which are reduced by cotransfection with the dominant negative forms of JNK and SEK. The Elk-driven construct (B) displays background levels of transcription in the absence of cotransfected kinase MEK1. Error bars indicate SD.