UBC and cystic fibrosis: To that end we introduced 4 of the most common CF-causing PTCs (G542XUGA, R553XUGA, R1162XUGA, and W1282XUGA), which represent ∼75% of all CF-causing PTCs, into a construct containing CFTR cDNA with appended C-terminal Nluc expressed from a short ubiquitin C (UbC) promoter (Figure 7A).