TRANSCRIPTION FACTOR VERACITY - IS GBF3 RESPONSIBLE FOR ABA-REGULATEDEXPRESSION OF ARABIDOPSIS ADH

Assignment of particular transcription factors to specific roles in pr omoter elements can be problematic, especially in systems such as the G-box, where multiple factors of overlapping specificity exist, In the Arabidopsis alcohol dehydrogenase (Adh) promoter, the G-box regulates expression in response to cold and dehydration, presumably through th e action of abscisic acid (ABA), and is bound by a nuclear protein com plex in vivo during expression in cell cultures. In this report, we te st the conventional wisdom of biochemical approaches used to identify DNA binding proteins and assess their specific interactions by using t he G-box and a nearby half G-box element of the Arabidopsis Adh promot er as a model system. Typical in vitro assays demonstrated specific in teraction of G-box factor 3 (GBF3) with both the G-box and the half G- box element, Dimethyl sulfate footprint analysis confirmed that the in vitro binding signature of GBF3 essentially matches the footprint sig nature detected in vivo at the G-box, Because RNA gel blot data indica ted that GBF3 is itself induced by ABA, we might have concluded that G BFB is indeed the GBF responsible in cell cultures for binding to the Adh G-box and is therefore responsible for ABA-regulated expression of Adh. Potential limitations of this conclusion are exposed by the fact that other GBFs bind the G-box with the same signature as GBF3, and s ubtle differences between in vivo and in vitro footprint signatures in dicate that factors other than or in addition to GBF3 interact with th e half G-box element.