The 5-upstream region of the class I patatin gene B33 directs strong expression of the -glucuronidase (GUS) reporter gene in potato tubers and in leaves treated with sucrose. Cis-acting elements affecting specificity and level of expression were identified by deletion analysis in transgenic potato plants. A putative tuber-specific element is located downstream from position –195. Nuclear proteins present in leaf and tuber extracts bind specifically to a conserved AT rich motif within this region. A DNA fragment between –183 and –143, including the binding site is, however, not able to enhance the expression of a truncated 35S promoter from cauliflower mosaic virus. Independent positive elements contributing to a 100-fold increase relative to the basic tuber-specific element are located between –228 and –195; –736 and –509, –930 and –736 and –1512 and –951. Sucrose inducibility is controlled by sequences downstream of position –228, indicating that the tuber-specific and sucrose-inducible elements are in close proximity.