When a plasmid encoding the Sleeping Beauty (SB) transposase (pCMV-SB) was cointroduced with luciferase expression plasmid DNA into Mouse skeletal muscle at a molar ratio of 4:1. luciferase gene expression was 5-times higher than the expression Without pCMV-SB on day 28. This enhancement was not dependent on the presence of transposon (Tn) sequence in luciferase expression plasmid. southern blot analysis failed 10 detect luciferase gene insertion into the host genome. Then, expression, a luciferase expression plasmid without Tn was cointroduced into HcLa cells with or without pCMV-SB. With pCMV-SB, the mRNA amount and the luciferase activity was 1.5 times and 2 times higher. respectively, than without pCMV-SB, even though the cells with pCMV-SB had a smaller copy number of luciferase plasmid than the cells without pCMV-SB. These results Suggest that SB transposase enhances the transcription of an exogenous gene regardless of the presence of the Tn sequence. (C) 2004 Elsevier Inc. All rights reserved.