NUCLEAR-PROTEIN FACTORS BINDING TO A CLASS-I PATATIN PROMOTER REGION ARE TUBER-SPECIFIC AND SUCROSE-INDUCIBLE

Genes encoding patatin, the major storage protein of the potato tuber, are generally divided into two classes, class I and class II, The exp ression of the class I patatin genes is normally tuber-specific, but c an be induced in leaves by high concentrations of sucrose. By employin g electrophoretic mobility shift assays (EMSA), we have identified nuc lear protein factors that interact specifically with the proximal port ion of the class I patatin promoter that is required for tuber-specifi c and sucrose-inducible expression. The factors were detected in nucle ar extracts prepared from potato tubers and sucrose-induced leaves, bu t not in extracts from leaves of normal potato plants. Four putative t ranscription factor-binding sites were localized using DNase I footpri nting. Competitive EMSA was employed to show that the same protein fac tor binds to at least two of the sites (boxes D and M). Interestingly, these two binding sites are highly homologous to light-responsive ele ments present in genes for the ribulose-1,5-bisphosphate carboxylase s mall subunit.