Identification of an IRES element in the coding region of Cx55.5 using Di-cis vectors. A) Schematic map of the pRF-Di cis vector having Renilla luciferase (RLuc) as the first cistron and Firefly luciferase (FLuc) as the downstream cistron, with two stable stem-loops or hairpins (HP), one at the 5' end and another at 3' end of Renilla luciferase gene. pRF-IR1 construct carrying the coding region (from nt631 to nt1200) of the CT in the intercistronic region, and pRF-IR2 construct with the coding region (from nt631 to nt990) of the CT in the intercistronic region. B) IRES activity of the above three constructs in N2A, HeLa and NIH3T3 cells. The IRES activity is represented as ratio of Firefly to Renilla luciferase activity (FLuc/RLuc) with the activity of the control vector, pRF-Di cis set is at 1. Each construct was tested five times and each experiment was done in triplicate. Data are expressed as mean ± SEM.