Abstract
We have identified two closely related human proteins (sigma3A and sigma3B) that are homologous to the small chains, sigma1 and sigma2, of clathrin-associated adaptor complexes. Northern and Western blot analyses demonstrate that the products of both the sigma3A and sigma3B genes are expressed in a wide variety of tissues and cell lines. sigma3A and sigma3B are components of a large complex, named AP-3, that also contains proteins of apparent molecular masses of 47, 140 and 160 kDa. In non-neuronal cells, the 47 kDa protein most likely corresponds to the medium chain homolog p47A, and the 140 kDa protein is a homolog of the neuron-specific protein beta-NAP. Like other members of the medium-chain family, the p47A chain is capable of interacting with the tyrosine-based sorting signal YQRL from TGN38. Immunofluorescence microscopy analyses show that the sigma3-containing complex is present both in the area of the TGN and in peripheral structures, some of which contain the transferrin receptor. These results suggest that the sigma3 chains are components of a novel, ubiquitous adaptor-like complex involved in the recognition of tyrosine-based sorting signals.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adaptor Protein Complex 1*
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Adaptor Protein Complex 2*
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Adaptor Protein Complex sigma Subunits*
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Adaptor Proteins, Vesicular Transport
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Amino Acid Sequence
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Blotting, Northern
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Blotting, Western
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Cells, Cultured
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Clathrin / metabolism
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Cloning, Molecular
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Cytosol / chemistry
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Cytosol / metabolism
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Fluorescent Antibody Technique
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Gene Expression
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Glycoproteins*
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Golgi Apparatus / chemistry*
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Humans
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Membrane Glycoproteins / metabolism
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Membrane Proteins / chemistry
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Membrane Proteins / metabolism
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Microscopy, Fluorescence
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Molecular Sequence Data
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Monomeric Clathrin Assembly Proteins*
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Nerve Tissue Proteins / analysis
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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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Phosphoproteins / analysis
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Phosphoproteins / chemistry*
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Phosphoproteins / genetics
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Phosphoproteins / metabolism*
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Phosphorylation
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Sequence Alignment
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Signal Transduction / physiology
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Transformation, Genetic / genetics
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Tyrosine / metabolism
Substances
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AP1S1 protein, human
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AP2S1 protein, human
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Adaptor Protein Complex 1
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Adaptor Protein Complex 2
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Adaptor Protein Complex sigma Subunits
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Adaptor Proteins, Vesicular Transport
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Clathrin
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Glycoproteins
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Membrane Glycoproteins
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Membrane Proteins
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Monomeric Clathrin Assembly Proteins
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Nerve Tissue Proteins
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Phosphoproteins
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TGOLN2 protein, human
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adaptor protein complex 1, sigma 1 subunit
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clathrin assembly protein AP180
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Tyrosine