Abstract
IMP1 encodes a subunit of the mitochondrial inner membrane peptidase responsible for the proteolytic processing of cytochrome oxidase subunit 2 (Cox2) and cytochrome b2 (Cytb2). The molecular defect in an imp1 mutation and the characterisation of a high-copy-number suppressor is described. A deletion of the suppressor region causes respiration deficiency. The DNA sequence revealed three very small overlapping ORFs. Constructs which carried termination codons within the ORFs or lacked ATG initiation codons still retained complementing activity on a high-copy-number plasmid. Nevertheless, the possibility that the suppressor acts at DNA or RNA level could be excluded. Subcloning of the ORFs, complementation analysis in low-copy-number plasmids and transcript mapping identified the 222 bp ORF as the suppressor gene designated SOM1. The SOM1 gene is transcribed into a 375 bp polyadenylated RNA and the deduced amino acid sequence predicts a small protein of 8.4 kDa with no significant sequence similarity to known proteins. In the som1 deletion mutant, proteolytic processing of the Cox2 precursor is prevented and Cytb2 is strongly reduced. SOM1 represents a new small gene which encodes a novel factor that is essential for the correct function of the Imp1 peptidase and/or the protein sorting machinery.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Amino Acid Sequence
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Aspartic Acid / genetics
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Base Sequence
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Cell Membrane / enzymology
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Chromosome Mapping
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DNA, Mitochondrial / genetics*
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Electron Transport Complex IV / genetics
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Electron Transport Complex IV / metabolism
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Endopeptidases / genetics*
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Endopeptidases / metabolism
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Enzyme Stability
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Fungal Proteins / genetics*
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Fungal Proteins / metabolism
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Gene Deletion
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Gene Expression Regulation, Fungal
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Gene Frequency
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Genes, Fungal*
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Genes, Suppressor
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Glycine / genetics
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L-Lactate Dehydrogenase (Cytochrome)
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L-Lactate Dehydrogenase / genetics
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L-Lactate Dehydrogenase / metabolism
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Membrane Proteins*
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Mitochondrial Proteins
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Molecular Sequence Data
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Mutation
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Peptide Hydrolases
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RNA, Fungal
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Repressor Proteins / genetics*
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Repressor Proteins / metabolism
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Saccharomyces cerevisiae / enzymology
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Saccharomyces cerevisiae / genetics*
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Saccharomyces cerevisiae Proteins*
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Sequence Analysis, DNA
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Serine Endopeptidases / genetics*
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Serine Endopeptidases / metabolism
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Transcription, Genetic
Substances
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DNA, Mitochondrial
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Fungal Proteins
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Membrane Proteins
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Mitochondrial Proteins
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RNA, Fungal
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Repressor Proteins
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SOM1 protein, S cerevisiae
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Saccharomyces cerevisiae Proteins
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Aspartic Acid
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L-Lactate Dehydrogenase
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L-Lactate Dehydrogenase (Cytochrome)
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Electron Transport Complex IV
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Endopeptidases
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Peptide Hydrolases
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Serine Endopeptidases
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type I signal peptidase
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IMP1 protein, S cerevisiae
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Glycine