DNase I and micrococcal nuclease analysis of the tomato proteinase inhibitor I gene in chromatin.

The chromatin structure of the wound-inducible proteinase inhibitor I gene was investigated in nuclei from leaves of wounded and unwounded tomato plants. DNase I digestion of intact nuclei revealed that the inhibitor I chromatin structure was highly sensitive to the enzyme compared to the inactive ribosomal chromatin. This sensitivity was independent of wounding. Digestion of tomato nuclei with micrococcal nuclease, which produces a nucleosomal ladder from bulk chromatin in agarose gels, supported these observations. Micrococcal nuclease produced only a faint nucleosomal repeat superimposed on a smear for the coding region of the inhibitor I gene, whereas digestion of inactive ribosomal chromatin produced a well defined nucleosomal ladder. Two DNase I-hypersensitive sites were found in the promoter region of the inhibitor I gene. Both were present before and after wound induction. These two constitutive DNase I-hypersensitive sites may correspond to DNA regulatory regions of the gene. The combined results indicate the existence of an open chromatin conformation in the inhibitor I gene DNA region, present before gene induction by wounding.