title: Alternative processing of Arabidopsis Hsp70 precursors during protein import into chloroplasts.
abstract: During protein import into chloroplasts, one of the Hsp70 proteins in pea (Hsp70-IAP), previously reported to localize in the intermembrane space of chloroplasts, was found to interact with the translocating precursor protein but the gene for Hsp70-IAP has not been identified yet. In an attempt to identify the Arabidopsis homolog of Hsp70-IAP, we employed an in vitro protein import assay to determine the localization of three Arabidopsis Hsp70 homologs (AtHsp70-6 through 8), predicted for chloroplast targeting. AtHsp70-6 and AtHsp70-7 were imported into chloroplasts and processed into similar-sized mature forms. In addition, a smaller-sized processed form of AtHsp70-6 was observed. All the processed forms of both AtHsp70 proteins were localized in the stroma. Organelle-free processing assays revealed that the larger processed forms of both AtHsp70-6 and AtHsp70-7 were cleaved by stromal processing peptidase, whereas the smaller processed form of AtHsp70-6 was produced by an unspecified peptidase.
authors.affiliation: The United Graduate School of Agricultural Sciences, Ehime University, Matsuyama, Japan.
authors.forename: R M Udayangani
authors.initials: RM
authors.lastname: Ratnayake
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Inoue
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nonami
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Akita
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism; D017360:Arabidopsis / Q000166:cytology* / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D019295:Computational Biology; D005998:Glycine; D018840:HSP70 Heat-Shock Proteins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism*; D011498:Protein Precursors / Q000737:chemistry / Q000378:metabolism*; D021381:Protein Transport; D013997:Time Factors; D014357:Trypsin / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D018840:HSP70 Heat-Shock Proteins; D010940:Plant Proteins; D011498:Protein Precursors; D014357:Trypsin; D005998:Glycine