DNA conformation may be an important factor affecting gene transcription. In this study, we examined how DNA sequences with unusual conformations affect transgene expression. A(30) and (CG)(15) sequences that can adopt the B' and Z conformations, respectively, were introduced into a beta-actin promoter. Luciferase plasmids containing the manipulated promoter were transfected into NIH3T3 cells by electroporation and were delivered into mouse livers with a hydrodynamics-based injection. Expression from plasmid with the (CG)(15) sequence was multiple times higher than expression from control plasmid DNA. The A(30) sequence also tended to enhance expression. These results suggest that non-B DNA sequences could improve transgene expression in cells. (C) 2009, The Society for Biotechnology, Japan. All rights reserved.