The uptake by HeLa cells of fluorescein - labelled pDNA complexed with LPEI or HIS revealed that the cell fluorescence associated with p3NF - luc-3NF and pCMVluc were quite comparable after 5 h incubation whatever the polymer used ( Figure 1 insert ) . Compared to pCMVluc , the remarkable effect on the luciferase gene observed in Figure 1 with p3NF - luc-3NF may be likely due to a larger number of pDNA copies imported into the nucleus .   This could imply that the weakness of the TATA - like promoter in p3NF - luc-3NF was counterbalanced by the higher number of pDNA copies in the nucleus . The cell fluorescence associated with pTAL - luc was a third ( with LPEI ) to a fifth ( with HIS ) less than that with p3NF - luc-3NF , suggesting that pTAL - luc polyplexes were slightly less taken up by the cells . Nevertheless , this uptake difference can not explain the 1300 - fold higher luciferase activity observed with p3NF - luc-3NF compared to pTALluc ( Figure 1 ) . This could be consecutive to an enhancement of the 3NF - plasmids penetration in the nucleus . Similar results were obtained with C2C12 cells except that the cell - associated fluorescence was 2 - to 3 - fold higher than with HeLa cells ( data not shown ) .