A cDNA encoding a metallothionein I-like protein from coffee leaves (Coffea arabica).

Metallothioneins are small, high-Cys-containing proteins present in a wide variety of organisms including vertebrates, invertebrates, fungi, cyanobacteria, and higher plants (Hamer, 1986). Metallothioneins play a role in heavy metal detoxification, especially in respect to cadmium, copper, and zinc (Hamer, 1986). Gene disruptions of the bakers’ yeast Cupl locus that encodes a metallothionein and the mouse metallothionein I and I1 genes result in hypersensitivity to copper and cadmium (Hamer et al., 1985; Michalska and Choo, 1993). Metallothioneins might also be involved in regulation of cellular availability of required heavy metals, especially copper and zinc (Hamer, 1986). Metallothionein-like proteins and genes have been isolated from a number of higher plants, including both monocots and dicots (Lane et al., 1987; De Framond, 1991; Kawashima et al., 1991; Robertson et al., 1992; Zhou and Goldsbrough, 1994; K. Takahashi, GenBank accession No. X62818; Weig and Komor, GenBank accession No. L02306). Plant metallothioneins are also involved in heavy metal tolerance. Evans et al. (1992) have shown that expression of a pea metallothionein-like gene using a cauliflower mosaic virus 35s promoter to drive expression results in increased accumulation of copper in transgenic Arabidopsis thaliana. In addition, two different A. thaliana metallothioneins are capable of complementing a deletion of the bakers’ yeast metallothionein gene Cupl (Zhou and Goldsbrough, 1994). This is consistent with a role in heavy metal detoxification. Also, in wheat high levels of metallothionein are found in embryos, as might be expected if it has a role in metal ion homoeostasis (Kawashima et al., 1992). We now report the isolation of a full-length cDNA from immature coffee (Coffea arabica) leaves encoding a metallothionein I-like protein (Table I). The deduced coding region encodes an 80-amino acid protein with 64% identity to a Ricinus communis metallothionein. One unusual characteristic of this cDNA is a 684-base 3’ untranslated region. The A. thaliana and R. communis metallothionein ml7NAs also