The effect of coexpression of +-MITF or mi-MITF cDNA on the luciferase activity under the control of the Gr B gene promoter. Various forms of the reporter and effector constructs were introduced into P-815 cells by electroporation. Three solid squares represent CANNTG motifs between nt −910 and +42; ie, CAGATG (nt −563 to −558), CACGTG (nt −530 to −525), and CATTTG (nt −521 to −516) motifs. The bars represent the mean ± standard error (SE) of the relative luciferase activities obtained by three independent experiments: (▪) +-MITF; (□) mi-MITF; (▨) pEF-BOS. In some cases, the SE was too small to be shown by the bars. *P< .01 by t-test when compared with the luciferase activity, in which pEF-BOS containing no insert was cotransfected.