SCAFFOLD ATTACHMENT REGIONS INCREASE REPORTER GENE-EXPRESSION IN STABLY TRANSFORMED PLANT-CELLS

The yeast ARS-1 element contains a scaffold attachment region (SAR) th at we have previously shown can bind to plant nuclear scaffolds in vit ro. To test effects on expression, constructs in which a chimeric beta -glucuronidase (GUS) gene was flanked by this element were delivered i nto tobacco suspension cells by microprojectile bombardment. In stably transformed cell lines, GUS activity averaged 12-fold higher (24-fold on a gene copy basis) for a construct containing two flanking SARs th an for a control construct lacking SARs. Expression levels were not pr oportional to gene copy number, as would have been predicted if the el ement simply reduced position effect variation. Instead, the element a ppeared to reduce an inhibitory effect on expression in certain transf ormants containing multiple gene copies. The effect on expression appe ars to require chromosomal integration, because SAR constructs were on ly twofold more active than the controls in transient assays.