The human elongation factor 1 alpha (EF-1α) first intron highly enhances expression of foreign genes from the murine cytomegalovirus promoter

In order to develop a highly efficient mammalian expression vector, we constructed a vector by the combination of the murine cytomegalovirus (MCMV) immediate early (IE) promoter and the human elongation factor one alpha (EF-1α) first intron. The MCMV IE promoter was several fold stronger than the human cytomegalovirus (HCMV) immediate early (IE) promoter and the human elongation factor one alpha (EF-1α) promoter in various mammalian cell lines such as NIH3T3, Neuro-2a, 293T or HT1080 and was only slightly weaker than the HCMV or the EF-1α promoter in HeLa and CHO cell lines. We inserted the first intron of the human EF-1α gene behind the MCMV and the HCMV promoter to enhance the gene expression through increasing RNA transcription and/or RNA stability. The insertion of the human EF-1α first intron markedly enhanced the level of gene expression in many cell lines and the resultant MCMV promoter with the human EF-1α first intron (MCMV/EF-I) was higher than the HCMV promoter from 4.3 to 65.5-fold in various cell lines. Also, the MCMV/EF-I promoter induced higher level of erythropoietin expression than the HCMV promoter in transiently transfected CHO cells.