Structure and organization of the human metaxin gene (MTX) and pseudogene.
Metaxin encodes a mitochondrial protein and is an essential nuclear gene in mice. The cDNA sequence and genomic organization of the human metaxin gene (MTX) have now been determined. MTX is 6 kb and consists of eight protein-encoding exons. The gene is contiguous to thrombospondin 3 (THBS3) and to the pseudogene for glucocerebrosidase (psGBA), but it transcribed in a direction opposite to the latter two genes. Thus, MTX and THBS3 share a common promoter region and are transcribed convergently, whereas MTX and psGBA are transcribed convergently and have closed apposed polyadenylation sites. Human metaxin contains 317 amino acids and is 91.5% identical to mouse metaxin. Metaxin is rich in leucine (14.2%) and in basic (12.9%) and acidic (12.0%) amino acids. The predicted protein lacks an amino-terminal signal sequence and N-glycosylation sites, but contains a putative transmembrane domain near its carboxy terminus. A DNA duplication has led to a direct repeat and the evolution of a pseudogene for GBA. A pseudogene for metaxin (psMTX) is also located within the 16 kb of DNA separating GBA from psGBA. The psMTX sequence is nearly identical to the 3' part of exon 2 through exon 8 of MTX, and both the intronic and the 3'-flanking sequences are highly conserved. Thus, there is a 278 amino acid open reading frame that is 97.8% identical to metaxin. However, psMTX lacks the first intron and promoter present in MTX, and at least in liver, the pseudogene is not expressed.
Long
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Department of Biochemistry, University of Washington, Seattle 98195, USA.
Winfield
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Adolph
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Ginns
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Bornstein
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D018076:DNA, Complementary; D006801:Humans; D051379:Mice; D033681:Mitochondrial Membrane Transport Proteins; D008969:Molecular Sequence Data; D011506:Proteins / Q000235:genetics*; D011544:Pseudogenes; D012045:Regulatory Sequences, Nucleic Acid
D018076:DNA, Complementary; C093550:MTX1 protein, human; D033681:Mitochondrial Membrane Transport Proteins; C490556:Mtx1 protein, mouse; D011506:Proteins