FIG. 1.

TnI SURE reporter constructs used in this study. Wild-type SURE (−868 to −741) and all its derivatives were placed upstream of the −95 TnIs basal promoter driving firefly luciferase in pGL3Basic. The shortest SURE deletion (SURE-807) terminates upstream of the CACC box and contains three of the four motifs conserved between SURE and FIRE (CACC, MEF-2, and E box). The boxed area between the MEF-2 site and E box harbors a sequence that conforms to an NFAT element. In SURE-827, 20 bp of the upstream sequence was added back to SURE-807 to obtain a truncated enhancer that includes the CAGG motif in addition to the aforementioned sites. SURE-842 and SURE-857 also contain the BLM (GTTAATCCG), which is not found in FIRE. On the opposite strand, this sequence resembles an initiator element (32, 55). The FIRE-SURE enhancer was generated by fusing the 5′ half of FIRE (from +776 to +714) to the 3′ half of SURE (from −807 to −741), resulting in a chimeric enhancer with a preserved spatial organization of all four conserved motifs.