According to the rules of eukaryotic gene expression and regulation,two versatile eukaroytic expression vectors(pMAML1-dhfr and pMAML2-dhfr) originated from pSV2-dhfr were constructed.They both have a CMV immediate early promoter/enhancer and consist of two expression units of parallel or opposite orientation.Using firefly luciferase gene as reporter gene and β-galactosidase gene as internal control,their effects on luciferase expression were studied in COS-7 transient expression system.The relative strength of their cis-elements were compared with those in pSV2-dhfr.