A DNA-binding activity for the promoter of the gene encoding C-4 phosphoenolpyruvate carboxylase is modulated by phosphorylation during greening of the Sorghum leaf

Electrophoresis mobility shift assay (EMSA) identified nuclear proteins wit h binding activity to a 430 bp promoter fragment of the Sorghum C-4 phospho enolpyruvate carboxylase gene (SvC4). The DNA binding activities (two main retarded bands; PCI and PC2) were high in nuclear extracts from etiolated l eaves, decreased during greening and became very low or null in nuclear ext racts from green leaves. This process was found to be mediated by phytochro me and was apparently irreversible since the DNA-binding activities were no t restored in green plants kept in continuous darkness. The AT-rich region of the promoter fragment was identified to be the interaction domain of PC2 . The detection of PC2 with EMSA was markedly reduced by preincubation of n uclear protein extracts with Mg-ATP or Mg-GTP and restored in the presence of a general protein serine/threonine-kinase inhibitor, K252a. The results suggested that the PC2 binding activity was modulated by phosphorylation du ring the greening process of the Sorghum leaf. (C) 2000 Elsevier Science Ir eland Ltd. All rights reserved.