Deletion of polypyrimidine tract elements reveal a significant reduction in IRES mediated activitys of Cx55.5. A) Partial DNA sequence of the Cx55.5 IRES element with polypyrimidine tract 1 (PPT1) and polypyrimidine tract 2 (PPT2) (underlined by bars) is depicted. The relative position of each element relative to the start nucleotide of the Cx55.5 coding region is shown. B) Schematic representation of the Di-cis constructs applied: pRF, control vector having Rennila luciferase as first cistron (RLuc) and Firefly luciferase as downstream cistron (FLuc) with the first cistron under the control of the CMV promoter activity. pRF-IR; wild type IRES containing Di-cis construct, with the IRES element placed between first and second cistron. pRF-IRDel1 = PPT1 deleted, pRF-IRDel2 = PPT2 deleted, pRF-IRDel3 = PPT1, PPT2 and the intervening sequence deleted. HP = hairpin structure C) IRES activity of the constructs in transiently transfected N2A cells. IRES activity is represented as the ratio of Firefly to Rennila luciferase activities (FLuc/RLuc) with the activity of control vector set to "1". Each construct was tested 4 times and each experiment was done in triplicates. Data are represented as mean of ± SEM.