PCK2 and cancer: Next, expression vectors encoding hTERT-targeting ribozymes harboring the suicide gene (herpes simplex virus thymidine kinase, HSVtk) as the 3′ exon and 122aT in the 3′-UTR under the control of cytomegalovirus (CMV) or liver-specific phosphoenolpyruvatecarboxykinase (PEPCK) promoter (CRT-122aT and PRT-122aT, respectively) were constructed to develop trans-splicing ribozymes with the ability to selectively trigger therapeutic transgene activity in hTERT(+) cancer cells, but not in normal liver cells (Fig. 2A).