HTLV-1 Tax trans-activates the IL-13 promoter in transiently transfected Jurkat T cells. (A) Luciferase reporter plasmids containing the human IL-13 promoter element extending 357 bp (pD3397), 155 bp (pD3402), or 67 bp (pD3403) upstream of the RNA start site are shown. Locations of the promoter-proximal NFAT and GATA3 sites are indicated. (B) Jurkat T cells were cotransfected with the indicated IL-13 promoter reporter plasmids and either a Tax expression plasmid (▪) or an empty expression vector (□). Luciferase activity was determined in cell extracts prepared 48 hours after transfection and is expressed as the percent of the activity obtained in cells transfected with pCMV-luc. The data represent the mean of 5 independent transfection experiments with standard deviations indicated by error bars.