Effect of GAL4-tagged p68 and p72 on transcriptional activity as measured by CAT assays using the TK-CAT, MLP-CAT and SV40-CAT promoter-reporter plasmids, each harbouring 5 copies of a GAL4 binding site fused to the promoter. The pcDNA3-GAL4 expression vector (pcG4) was used as a control. In each case U2OS cells were co-transfected with pcG4 or plasmids expressing GAL4-tagged p68/p72 (p68G4/p72G4) and the appropriate promoter-reporter construct. The amounts of DNA transfected were: pcG4-, p68G4-/p72G4- 1 μg; TK-CAT- 2.5 μg; MLP-CAT- 9 μg; SV40-CAT- 0.5 μg. The amount of DNA used had been previously titrated to achieve appropriate levels of baseline CAT activity. a) Transcriptional repression by p68 and p72 as measured by CAT activity, which is shown as % conversion of 14C-labelled chloramphenicol to acetylated forms. The data represent results from 5 independent assays, which were each performed in triplicate. b) Western blot, using a GAL4-specific antibody, showing expression levels of the pcG4, p68G4 and p72G4 plasmids.