Importance of SV40 early 5′ distal sequences in directing heterologous gene expression

The chloramphenicol acetyltransferase-encoding reporter gene ( cat ) is used extensively in assessing the ability of transcriptional regulatory elements ( TRE ) to direct gene expression in eukaryotic cells. Two commonly utilized plasmids contain the cat coding sequences under the transcriptional control of the Rous sarcoma virus LTR (pRSV cat ) or simian virus 40 early (SV40E) promoter (pSV2 cat ). In the present study, we have recloned the RSV-LTR and SV40E TRE into a pUC18 vector. Direct comparison of these TRE in different plasmid vectors, as well as reevaluation of their relative level of cat expression revealed: ( 1 ) a small but significant increases in SV40E-directed reporter gene expression was observed when the TRE was inserted into the pUC18 vector; and ( 2 ) a significant increase in SV40E-directed gene expression was realized by inclusion of the 69-bp 5′ of the sequences present in pSV2 cat . These distal sequences are required for maximal activity of the SV40 TRE in the cell lines tested.