title: The 5'-leader sequence of sugar beet mitochondrial atp6 encodes a novel polypeptide that is characteristic of Owen cytoplasmic male sterility.
abstract: Cytoplasmic male sterility (CMS) is a mitochondrially encoded trait, which is characterized by a failure of plants to produce viable pollen. We have investigated the protein profile of mitochondria from sugar beet plants with normal (fertile) or CMS cytoplasm, and observed that a 35-kDa polypeptide is expressed in Owen CMS plants but not in normal plants. The variant 35-kDa polypeptide was found in CMS mitochondria placed in five different nuclear backgrounds. Interestingly, this polypeptide proved to be antigenically related to a 387-codon ORF (preSatp6) that is fused in-frame with the downstream atp6. The presequence extension of the atp6 ORF is commonly found in higher plants, but whether or not it is normally expressed has hitherto remained unclear. Our study is thus the first to demonstrate that the atp6 presequence is actually translated in mitochondria. We also observed that preSATP6 is a mitochondrial membrane protein that assembles into a homogeneous 200-kDa protein complex. In organello translation experiments in the presence of protease inhibitors showed a reduction in the abundance of mature preSATP6 with time, suggesting that the mature preSATP6 may be derived by proteolytic processing of a translation product of the preSatp6/Satp6 ORF.
authors.affiliation: Laboratory of Genetic Engineering, Graduate School of Agriculture, Hokkaido University, N-9, W-9, Kita-ku, Sapporo, 060-8589, Japan.
authors.forename: Masayuki P
authors.initials: MP
authors.lastname: Yamamoto
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Kubo
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Mikami
mesh_terms: D024506:5' Flanking Region / Q000235:genetics*; D000595:Amino Acid Sequence; D027461:Beta vulgaris / Q000235:genetics*; D015153:Blotting, Western; D004926:Escherichia coli; D005298:Fertility / Q000235:genetics; D015870:Gene Expression; D005822:Genetic Vectors / Q000235:genetics; D005982:Glutathione Transferase; D047468:Immunoprecipitation; D024101:Mitochondrial Proteins / Q000378:metabolism; D025261:Mitochondrial Proton-Translocating ATPases / Q000235:genetics*; D008969:Molecular Sequence Data; D010455:Peptides / Q000235:genetics* / Q000378:metabolism
chemical_list: D024101:Mitochondrial Proteins; D010455:Peptides; D005982:Glutathione Transferase; D025261:Mitochondrial Proton-Translocating ATPases