Water de®cit has a signi®cant impact on patterns of gene expression. Based on the deduced amino acid sequence, it has been proposed that the drought and abscisic acid-induced gene (his1-s) of tomato (Lycopersicon esculentum Mill.) encodes an H1 histone variant. To study the role of H1-S it is important to understand the expression characteristics of the protein. To identify the his1-s product in vivo the his1-s cDNA was fused to a (His)6 tag and overexpressed in Escherichia coli. The H1-S fusion protein was used to generate an antibody that recognized a protein with an apparent molecular weight of 31 kDa that accumulates in response to water de®cit in the whole plant and detached leaves. A time course of his1-s expression showed that protein accumulation is delayed compared to the mRNA accumulation in both the whole plant and detached leaves. Cellular fractionation, immuno¯uores- cence and H1-S::b-glucuronidase fusion analyses in transgenic tissues were used to determine the cellular localization of H1-S. The results showed that H1-S accumulates in nuclei and is associated with chromatin of wilted tomato leaves. The drought- and abscisic acid- induced gene his1-s encodes a linker-histone subtype speci®cally accumulated in the nuclei and chromatin of tomato leaves subjected to water-de®cit conditions. Although the molecular mechanism of H1-S function is still unclear, the expression characteristics of H1-S are consistent with a potential role of this protein in the regulation of gene expression in response to water de®cit.
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