Abstract
Identification of all the protein components of the large subunit (39 S) of the mammalian mitochondrial ribosome has been achieved by carrying out proteolytic digestions of whole 39 S subunits followed by analysis of the resultant peptides by liquid chromatography and mass spectrometry. Peptide sequence information was used to search the human EST data bases and complete coding sequences were assembled. The human mitochondrial 39 S subunit has 48 distinct proteins. Twenty eight of these are homologs of the Escherichia coli 50 S ribosomal proteins L1, L2, L3, L4, L7/L12, L9, L10, L11, L13, L14, L15, L16, L17, L18, L19, L20, L21, L22, L23, L24, L27, L28, L30, L32, L33, L34, L35, and L36. Almost all of these proteins have homologs in Drosophila melanogaster, Caenorhabditis elegans, and Saccharomyces cerevisiae mitochondrial ribosomes. No mitochondrial homologs to prokaryotic ribosomal proteins L5, L6, L25, L29, and L31 could be found either in the peptides obtained or by analysis of the available data bases. The remaining 20 proteins present in the 39 S subunits are specific to mitochondrial ribosomes. Proteins in this group have no apparent homologs in bacterial, chloroplast, archaebacterial, or cytosolic ribosomes. All but two of the proteins has a clear homolog in D. melanogaster while all can be found in the genome of C. elegans. Ten of the 20 mitochondrial specific 39 S proteins have homologs in S. cerevisiae. Homologs of 2 of these new classes of ribosomal proteins could be identified in the Arabidopsis thaliana genome.
Highlights
Identification of all the protein components of the large subunit (39 S) of the mammalian mitochondrial ribosome has been achieved by carrying out proteolytic digestions of whole 39 S subunits followed by analysis of the resultant peptides by liquid chromatography and mass spectrometry
We have adopted a system of nomenclature in which proteins with prokaryotic homologs are given the same number as the corresponding ribosomal protein in E. coli (Table I)
The 17 ribosomal proteins described in this paper and the 31 previously characterized proteins increase the total number of proteins identified in mammalian mitochondrial 39 S subunits to 48
Summary
Identification of all the protein components of the large subunit (39 S) of the mammalian mitochondrial ribosome has been achieved by carrying out proteolytic digestions of whole 39 S subunits followed by analysis of the resultant peptides by liquid chromatography and mass spectrometry. 60 mammalian mitochondrial ribosomal proteins, 31 proteins from the large subunit and 29 proteins from the small subunit, have been characterized by different laboratories (2, 6 –14) The identification of these proteins used two approaches. Sequence information on the peptides present in this complex mixture was obtained by liquid chromatography coupled to tandem mass spectrometry (LC/MS/MS).1 This strategy allowed the identification of 28 proteins of the small subunit including 14 proteins that had not previously been identified [2]. 4 have homologs in prokaryotic ribosomes while 13 are members of new classes of large subunit ribosomal proteins
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