Subregion C shows an enhancer potential specific to cells of erythroid lineage. Transient transfection experiments were carried out using K562 cells, KATOIII cells, and fibroblasts. Transfection into K562 cells was performed using 2.5 μg of firefly luciferase reporter plasmid and 0.01 μg of pRL-SV40 Renilla luciferase reporter vector for each analysis. Transfection into KATOIII cells was carried out using 6 μg of firefly reporter and 0.01 μg of pRL-SV40 Renilla reporter. Transfection into fibroblasts was performed using 1 μg of firefly reporter and 0.01 μg of pRL-SV40 Renilla reporter. DNA fragment C between positions +5653 and +6154 was inserted upstream of the ABO promoter sequence in the same direction as that of the promoter in construct rC/SN, and in the opposite direction in construct C/SN. Arrows to the left represent the inserts oriented in a direction opposite to that of the promoter. To facilitate comparison of the corresponding reporter activity of each construct among the cells, the activity of the SN vector was assigned an arbitrary value of 1.0 in each cell line. The results are expressed as an average of the relative activity observed. The mean values and SDs were calculated from more than 3 independent experiments. Solid box indicates K562 cells; clear box, KATOIII cells; and gray box, fibroblasts.