Abstract
In vertebrates, assembly of spliceosomal uridine-rich small nuclear ribonucleoproteins (UsnRNPs) is mediated by the SMN complex, a macromolecular entity composed of the proteins SMN and Gemins 2-8. Here we have studied the evolution of this machinery using complete genome assemblies of multiple model organisms. The SMN complex has gained complexity in evolution by a blockwise addition of Gemins onto an ancestral core complex composed of SMN and Gemin2. In contrast to this overall evolutionary trend to more complexity in metazoans, orthologs of most Gemins are missing in dipterans. In accordance with these bioinformatic data a previously undescribed biochemical purification strategy elucidated that the dipteran Drosophila melanogaster contains an SMN complex of remarkable simplicity. Surprisingly, this minimal complex not only mediates the assembly reaction in a manner very similar to its vertebrate counterpart, but also prevents misassembly onto nontarget RNAs. Our data suggest that only a minority of Gemins are required for the assembly reaction per se, whereas others may serve additional functions in the context of UsnRNP biogenesis. The evolution of the SMN complex is an interesting example of how the simplification of a biochemical process contributes to genome compaction.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Cell Cycle Proteins / chemistry
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Cell Cycle Proteins / genetics
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Cell Cycle Proteins / metabolism
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Cell Line
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Cyclic AMP Response Element-Binding Protein / chemistry
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Cyclic AMP Response Element-Binding Protein / genetics*
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Cyclic AMP Response Element-Binding Protein / metabolism*
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Drosophila Proteins / biosynthesis*
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Drosophila Proteins / chemistry
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Drosophila Proteins / genetics*
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Drosophila Proteins / metabolism
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Drosophila melanogaster / genetics*
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Drosophila melanogaster / metabolism*
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Evolution, Molecular*
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Genome, Insect
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Histone Chaperones
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Intracellular Signaling Peptides and Proteins / chemistry
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Intracellular Signaling Peptides and Proteins / genetics
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Intracellular Signaling Peptides and Proteins / metabolism
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Models, Genetic
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Multiprotein Complexes
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Nerve Tissue Proteins / chemistry
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Nerve Tissue Proteins / genetics*
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Nerve Tissue Proteins / metabolism*
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RNA Splicing
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RNA-Binding Proteins / chemistry
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RNA-Binding Proteins / genetics*
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RNA-Binding Proteins / metabolism*
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Ribonucleoproteins, Small Nuclear / biosynthesis*
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Ribonucleoproteins, Small Nuclear / chemistry
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Ribonucleoproteins, Small Nuclear / genetics*
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SMN Complex Proteins
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Spliceosomes / metabolism
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Transcription Factors / chemistry
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Transcription Factors / genetics
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Transcription Factors / metabolism
Substances
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Cell Cycle Proteins
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Cyclic AMP Response Element-Binding Protein
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Drosophila Proteins
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Hira protein, Drosophila
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Histone Chaperones
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Intracellular Signaling Peptides and Proteins
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Multiprotein Complexes
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Nerve Tissue Proteins
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RNA-Binding Proteins
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Ribonucleoproteins, Small Nuclear
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Rig protein, Drosophila
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SMN Complex Proteins
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Transcription Factors