ANALYSIS OF THE INVOLVEMENT OF OCS-LIKE BZIP-BINDING ELEMENTS IN THE DIFFERENTIAL STRENGTH OF THE BIDIRECTIONAL MAS1'2' PROMOTER

The ocs-like elements of the bidirectional mas1'2' promoter of Agrobac terium tumefaciens, mas1' and mas2', were analyzed to elucidate their role in the expression conferred by this promoter. Tetramers of the el ements were cloned upstream of the B-glucuronidase-coding region linke d to the 35S promoter deleted at -54. Transient expression assays with tobacco (Nicotiana tabacum) and potato (Solanum tuberosum) protoplast s showed that tetramers of the mas1' element had 3- to 8-fold enhancin g activity, respectively. Enhancement obtained by tetramers of the mas 2' element was higher, suggesting that this element plays a role in th e stronger promoter activity from the 2' side. Three cDNA clones with high homology to the tobacco transcription factor TGA1a were isolated from a potato root expression library. Overexpression of the proteins encoded by these cDNA clones in Escherichia coli and analysis of DNA-b inding activity in bacterial extracts showed that all three factors co uld bind strongly to the mas1' ocs-like element. In contrast, only two of the mas-binding factors exhibited significant binding to the mas2' element. Southern analysis revealed the presence of a small, multigen e family encoding the mas-binding factors in potato.