Myb-dependent transcription is functionally impaired in clonal lines of HL-60 cells expressing c-Maf. HL-60 c-Maf clone 6 (▪) or CB6 vector control clone 3 (▨) were incubated at the indicated ZnSO₄ concentrations for 12 hours to induce c-Maf protein expression, and then transiently transfected with 5 μg of the −411luc reporter construct containing sequences sufficient for wild-type level, tissue-appropriate expression from theCD13/APN myeloid promoter. Luciferase activities were assayed at 6 hours and normalized for differences in transfection efficiency with SEAP activity produced by the control β-actin-SEAP plasmid.