hnRNP-K and Purα act together to repress theCD43 promoter.

The β-galactosidase expression construct pRSV-β was mixed with 1 of 4 different combinations of plasmids: (1) pHAPur1 and full-length hnRNP-K, which express Purα and hnRNP-K, respectively; (2) pHAPur1 and the empty vector equivalent of full-length hnRNP-K; (3) full-length hnRNP-K and pHA, which represents the empty vector equivalent of pHAPur1; and (4) both empty vectors. These 4 DNA mixtures were then transfected into the mixed pool of K562 cells containing theCD43/luciferase fusion and treated for 12 hours with PMA. Cells were harvested, lysed, and luciferase and β-galactosidase assays performed. The levels of β-galactosidase activity were taken as reflective of transfection efficiency and used to correct the luciferase assay results. Using these corrected values, the level of luciferase activity directed by the CD43 promoter in the presence of the empty vectors was assigned a value of 100%. The level of luciferase activity directed by the promoter in the presence of constructs expressing Purα or hnRNP-K was calculated as a proportion of the 100% value. The means of these levels ± SD resulting from 3 independent experiments are displayed as histograms.