Simian virus 40 early enhancer/promoter (SV40 early promoter)
Early promoter/enhancer region from simian virus 40 (SV40), constitutively active across a broad range of mammalian cell types. Weaker than the strongest viral and hybrid promoters but compact and reliable, commonly used to drive selection-marker genes (e.g., neomycin, puromycin resistance) in expression vectors so that a separate, stronger promoter can drive the gene of interest.
Origin: Simian virus 40 (SV40), early transcription unit
Characteristics
Contains the SV40 72 bp enhancer repeats and 21 bp GC-rich repeats upstream of the early transcription start sites; upstream sequences beyond 150 bp are indispensable for activity while the TATA box mainly fixes the precise start site rather than the expression level (Benoist & Chambon 1981). In a side-by-side lentiviral reporter comparison across eight mammalian cell lines, SV40 drives fairly strong but consistently lower expression than EF1A or CAG, and unlike the other five mammalian constitutive promoters tested it produces no detectable activity in Drosophila cell lines (Qin et al. 2010).
Applications: Used to drive selection-marker genes (neomycin/G418, puromycin, hygromycin resistance) in mammalian plasmid vectors, pairing a compact, dependable promoter with the marker while a separate stronger promoter drives the transgene of interest. Also used for moderate constitutive expression in transient transfection of standard cell lines such as HEK293 and COS.
Limitations: Weaker than EF1A, CAG, or CMV in most mammalian cell lines tested side by side, making it a poor choice when maximal expression of the gene of interest is the goal (Qin et al. 2010). Produces no detectable expression in Drosophila cell lines, unlike other mammalian constitutive promoters that retain some cross-species activity (Qin et al. 2010).
Sequence
References
- Qin et al. (2010). Systematic Comparison of Constitutive Promoters and the Doxycycline-Inducible Promoter. PLoS ONE - Qin 2010 Promoter Comparison