Transient transfection analysis of LF promoter gene plasmids. (A) Schematic diagram indicating the position of 5′ deletions of the LF promoter relative to the luciferase gene. (B) Luciferase activity of the LF promoter deletion plasmids transfected in K562 and HEL cells expressed as fold increase over luciferase activity measured for the promoterless pGL2-basic vector (background expression, which was consistently 100 to 200 RLU, was given a value of 1). Luciferase activity was normalized to β-galactosidase activity. The data represent 4 to 8 independent experiments each performed in duplicate for each promoter plasmid, and are expressed as the mean with SDs represented as error bars. (C) Luciferase activity of −726 bp, −916 bp, and −916(d)S LF promoter plasmids in uninduced 32Dcl3 cells. The −916(d)S plasmid was created by deletion of the underlined 56-bp fragment in (D). Luciferase activity was normalized to cotransfected β-galactosidase activity (pCMVβgal plasmid). The average of 3 independent experiments, each performed in duplicate, is presented. (D) The nucleotide sequence between the −916-bp and −728-bp coordinates of the LF promoter containing the triad octamers (overlined) and the 56-bp deletion (underlined) of the −916-bp plasmid to yield the −916(d)S plasmid.