Constitutive and light-induced DNAseI hypersensitive sites in the rbcS genes of pea (Pisum sativum)

The chromatin structure of pea (Pisum sativum) rbcS genes in inactive (root), potentially active (dark-grown leaf), and active states (light-grown leaf) was analysed using (a) pancreatic DNAseI to detect general DNAseI sensitivity and DNAseI-hypersensitive sites, and (b) methyl-sensitive restriction endonucleases to probe for cytosine methylation within the promoter region. We showed that within the same organ individual members of the pea rbcS multigene family are differentially sensitive to DNAseI suggesting differential protection in nuclei. During light activation general DNAseI sensitivity increases in some genes, especially their 5 upstream regulatory sequences. DNAseI-hypersensitive sites are constitutively present in 5 upstream regulatory sequences around positions –335, –465, –650, and –945 (5 constitutive domain) and in the coding region around position +340, +450, +530, +640, and +810 (3 constitutive domain). One additional hypersensitive site appears after light induction (inducible site). This region is centred around position –190 and flanked by light-responsive elements (LREs). In spite of changes in the chromatin structure of rbcS genes during their transition from an inactive to an active state, their cytosine methylation at Alu I, Fnu 4HI, Hae III, Sau 3AI and Sau 96I sites in the promoter region remains uniform.