An SAR sequence containing 395 bp DNA fragment mediates enhanced, gene-dosage-correlated expression of a chimaeric heat shock gene in transgenic tobacco plants.

A 395 bp fragment located downstream from the soybean heat shock gene Gmhsp 17.6-L exhibits several characteristics of scaffold attachment region (SAR) sequences. It contains matrix consensus elements, a topoisomerase II binding sequence and it associates with the isolated nuclear scaffold of soybean in vitro. Chimaeric genes containing the SARL fragment either at one side (5' or 3') or at both sides of a heat shock promoter-regulated beta-glucuronidase reporter gene were constructed. A five- to nine-fold increase of heat-inducible beta-glucuronidase activity was observed in transgenic tobacco plants containing constructs with SARL fragments either at both sides or with at least one SARL copy located upstream from the reporter gene. The gene copy number is positively correlated with the level of heat-inducible reporter gene activity in these plants but positional effects are not entirely eliminated. Thus, SAR sequences may potentially be used to increase gene expression, via as yet unknown mechanisms, and to reduce adverse effects on the expression of multiple gene copies in transgenic plants.