Lewin A, Mayer M, Chusainow J, Jacob D, Appel B (2005): Viral promoters can initiate expression of toxin genes introduced into Escherichia coli
BMC Biotechnol. 5 (1): 19 ff. [Epub ahead of print].

Background: The expression of recombinant proteins in eukaryotic cells requires the fusion of the coding region to a promoter that is functional in the eukaryotic cell line and viral promoters are very often used for this purpose. The initial cloning procedures are usually performed in Escherichia coli and therefore it is of interest to know whether the foreign promoter results in gene expression in the bacteria. In cases in which molecules toxic for humans are to be expressed, this knowledge would be indispensable for the specification of safety measures.

Results: We selected five frequently used viral promoters and quantified their activity in E. coli using a reporter system. Only the promoter from the thymidine kinase gene from HSV1 showed no activity, while the polyhedrin promoter from baculovirus, the early immediate CMV promoter, the early SV40 promoter and the 5' LTR promoter from HIV-1 all directed gene expression in E. coli. The determination of transcription start sites in the immediate early CMV promoter and the polyhedrin promoter confirmed the presence of bacterial -10 and -35 consensus sequences. The relevance of this heterologous gene expression for safety considerations was further confirmed by analysing fusions between these promoters and a promoter-less cytotoxin gene.

Conclusions: According to our results, a high percentage of viral promoters are able to initiate gene expression in E. coli. The degree of such heterologous gene expression can be sufficient for the expression of toxin genes and must therefore be considered when defining safety measures for handling corresponding genetically modified organisms.