摘要：Six plant MARs isolated from tobacco and Arabdiposis were investigated for their ARS activity in yeast. The results showed that among the six plant MARs, only TM1 and AM4 had strong ARS activity which was almost the same as that of ARS from yeast chromosome. In order to further identify the core region of the two MARs for the ARS activity, a series of subclones were created by PCR strategy, and the corresponding subclones were designated as TM1-1, TM1-2, TM1-3, AM4-1, AM4-2 and AM4-3, respectively. Our studies revealed that TMI-3 and AM4-3 not only had higher ARS activity, but also displayed higher transformation frequency, plasmid stability and growth rate compared to their intact MARs, TM1 and AM4. These data present an important clue for further elucidating the relationship between MAR and ARS.