Pea chloroplast DnaJ-J8 and Toc12 are encoded by the same gene and localized in the stroma.
Toc12 is a novel J domain-containing protein identified in pea (Pisum sativum) chloroplasts. It was shown to be an integral outer membrane protein localizing in the intermembrane space of the chloroplast envelope. Furthermore, Toc12 was shown to associate with an intermembrane space Hsp70, suggesting that Toc12 is important for protein translocation across the chloroplast envelope. Toc12 shares a high degree of sequence similarity with Arabidopsis (Arabidopsis thaliana) DnaJ-J8, which has been suggested to be a soluble protein of the chloroplast stroma. Here, we isolated genes encoding DnaJ-J8 from pea and found that Toc12 is a truncated clone of one of the pea DnaJ-J8s. Protein import analyses indicate that Toc12 and DnaJ-J8s possess a cleavable transit peptide and are localized in the stroma. Arabidopsis mutants with T-DNA insertions in the DnaJ-J8 gene show no defect in chloroplast protein import. Implications of these results in the energetics and mechanisms of chloroplast protein import are discussed.
Chiu
Chi-Chou
CC
Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan.
Chen
Lih-Jen
LJ
Li
Hsou-min
HM
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics; D002736:Chloroplasts / Q000235:genetics* / Q000378:metabolism; D017343:Genes, Plant; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009154:Mutation; D018532:Pisum sativum / Q000235:genetics* / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D021381:Protein Transport; D018749:RNA, Plant / Q000235:genetics; D011956:Receptors, Cell Surface / Q000235:genetics; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D029681:Arabidopsis Proteins; D010940:Plant Proteins; D018749:RNA, Plant; D011956:Receptors, Cell Surface; C495595:Toc120 protein, Arabidopsis