Enhanced cauliflower mosaic virus 35S (2×CaMV35S) promoter
Enhanced cauliflower mosaic virus 35S promoter (2×CaMV35S) containing a tandem duplication of the upstream enhancer domain fused to a single copy of the core promoter; drives constitutive transcription roughly 10-fold stronger than the standard single-enhancer CaMV35S promoter in transgenic plants. Used in Agrobacterium-mediated dicot transformation vectors when maximal constitutive expression is required.
Origin: Cauliflower mosaic virus (duplicated 35S enhancer)
Characteristics
Constructed by tandem duplication of the roughly 250 bp enhancer domain (approximately -343 to -90 relative to the transcription start site) placed upstream of an intact CaMV35S core promoter; the duplication increases transcriptional activity about 10-fold over the natural single-copy 35S promoter and acts as a strong enhancer of adjacent heterologous promoters (Kay et al. 1987). The duplicated domain corresponds to the tissue-preferential subdomain that drives expression mainly in leaves, stems, and cotyledons when tested alone (Benfey et al. 1989).
Applications: Used in place of standard single-enhancer CaMV35S in plant expression and reporter vectors for dicot species when higher transcriptional output is needed, including overexpression constructs and strong drivers for selectable marker or reporter genes delivered by Agrobacterium-mediated transformation.
Limitations: Larger than the standard CaMV35S promoter because of the duplicated enhancer element, adding to overall construct size. Like the parent CaMV35S promoter, it is markedly weaker in monocot species and inactive in pollen, so monocot transformation typically substitutes an intron-enhanced 35S derivative or a monocot-native promoter such as maize ubiquitin.