Us2 expression blocks ERK-mediated Elk-1 activation of transcription. (A) NIH 3T3 cells were cotransfected with a plasmid, pFA2-Elk1, that expresses the Elk-1 activation domain fused to the GAL4 DNA binding domain, a luciferase reporter plasmid, pFR-Luc, containing a synthetic promoter with five tandem repeats of the GAL4 binding site, and the combinations of plasmids indicated under the x axis. Luciferase activity, which is indicative of Elk1-dependent transcription, is expressed as relative light units. Note that the y axis has a log scale. (B) MRC-5 cells were cotransfected with pFA2-Elk1, pFR-Luc, and the combinations of plasmids indicated under the x axis. Error bars represent the standard deviations between experiments performed in triplicate. Variations in transfection efficiency were normalized by the inclusion of a beta-galactosidase reporter plasmid where expression is under control of a constitutively active promoter.