CaMV 35S minimal promoter
Part of the domain A of the CaMV 35S promoter, which contains the TATA box and extends from the -90 position to the transcription start site +1, is used by many as a “minimal promoter.” Apart from the TATA box, which is the binding site for RNA polymerase II, the region contains a least three CAAT-like boxes. These sequences potentiate the activity of upstream sequences and influence the efficiency of the promoter activity. These CAAT-like boxes alone, or attached to heterologous promoter regions, drive the expression of transgenes.
The so-called minimal promoter, which is often described as a sequence similar to that extending from nucleotides -60 or -46 to +1 of the 35S promoter, does not appear to drive the expression of a gene by itself. Additional sequences, such as an enhancer, are required. Thus, the 35S minimal promoter has often been used to find and define enhancer regions, and determine activity of heterologous promoters, and as part of trans-activating or inducible promoter systems.
A careful reading of the patents on the CaMV 35S promoter, including the ones directed to the subdomains of the promoter and the enhancer region, suggests but does not confirm that the widely used “minimal promoter” may be unencumbered by patents. The most relevant claims to the 35S minimal promoter were granted to the Rockefeller University in the patent US 5097025. Several independent claims cover the minimal promoter of the CaMV 35S promoter, which the inventors define as sequence from -46 to +8, but the minimal promoter is not claimed by itself, rather as linked to one of the subdomains of domain B of the 35S promoter
Because of the minimal amount of sequence actually derived from the 35S promoter, we suggest that scientists refer to it simply as a “minimal promoter.”