Nucleotide sequence of cDNA clone encoding a metallothionein-like protein from Chinese cabbage.

Abstract

Metallothionein is a low mo1 wt, Cys-rich metal-binding protein that is resistant to high levels of toxic metal ions by means of detoxification (Steffens, 1990). A full-length cDNA (pBIF 98) encoding the metallothionein-like protein was isolated from the inflorescence cDNA library of Chinese cabbage (Brassica campestris L. ssp. pekinesis). The nucleotide sequence has been determined using the dideoxynucleotide chain-termination method (Sanger et al., 1977) and the amino acid sequence deduced (Table I). The cDNA sequence is composed of 505 nucleotides, a putative open reading frame of 240 bp, a 5’ nontranslated sequence of 3 bp, and a 3’ noncoding region of 247 bp. The 3’ noncoding region contains the sequence AATATA 20 bp upstream from the polyadenylation site, which is homologous to the polyadenylation signal (AATAAA). Thr putative open reading frame encodes a protein of 80 residues (mo1 wt = 8108.82), which contains 14 Cys residues and three Cys-X-Cys or Cys-Cys clusters at the terminal region of the polypeptide. The regions of the Cys-X-Cys cluster at each terminal region are metal-binding domains. The domains are separated by an intervening sequence of amino acids like other metallothionein proteins (de Miranda et al., 1990). Comparison of this predicted protein with the protein identification resource protein data base (DNASIS software) shows 91.4, 47.4, 44.7, and 44.6% homology at the amino acid leve1 with metallothionein proteins of Arabidopsis thaliana (Protein Identification Resource accession No. S18069), garden pea (Evans et al., 1990), maize (de Framond, 1991), and barley (Okumura et al., 1991), respectively .