β3A-adaptin, a Subunit of the Adaptor-like Complex AP-3*
- From the Cell Biology and Metabolism Branch, NICHD, National Institutes of Health, Bethesda, Maryland 20892
Abstract
Recent studies have described a widely expressed adaptor-like complex, named AP-3, which is likely involved in protein sorting in exocytic/endocytic pathways. The AP-3 complex is composed of four distinct subunits. Here, we report the identification of one of the subunits of this complex, which we call β3A-adaptin. The predicted amino acid sequence of β3A-adaptin reveals that the protein is closely related to the neuron-specific protein β-NAP (61% overall identity) and more distantly related to the β1- and β2-adaptin subunits of the clathrin-associated adaptor complexes AP-1 and AP-2, respectively. Sequence comparisons also suggest that β3A-adaptin has a domain organization similar to β-NAP and to β1- and β2-adaptins. β3A-adaptin is expressed in all tissues and cells examined. Co-purification and co-precipitation analyses demonstrate that β3A-adaptin corresponds to the ∼140-kDa subunit of the ubiquitous AP-3 complex, the other subunits being δ-adaptin, p47A (now called μ3A) and ς3 (A or B). β3A-adaptin is phosphorylated on serine residues in vivo while the other subunits of the complex are not detectably phosphorylated. β3A-adaptin is not present in significant amounts in clathrin-coated vesicles. The characteristics of β3A-adaptin reported here lend support to the idea that AP-3 is a structural and functional homolog of the clathrin-associated adaptors AP-1 and AP-2.
Footnotes
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↵* The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) U81504.
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↵‡ To whom correspondence should be addressed: CBMB, NICHD, National Institutes of Health, Bldg. 18T, Rm. 101, 18 Library Dr. MSC 5430, Bethesda, MD 20892-5430. Tel.: 301-496-6368; Fax: 301-402-0078; E-mail:juan{at}helix.nih.gov.
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↵1 The abbreviations used are: RACE, rapid amplification of cDNA ends; BSA, bovine serum albumin; EST, expressed sequence tag; GST, glutathione S-transferase; PAGE, polyacrylamide gel electrophoresis; PCR, polymerase chain reaction; RT, reverse transcriptase; kb, kilobase pair(s).
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↵2 C. E. Ooi, J. E. Moreira, E. C. Dell’Angelica, G. Poy, D. Wassarman, and J. S. Bonifacino, submitted for publication.
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↵3 S. Lemmon and L. Robinson, personal communication.
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- Received February 24, 1997.
- Revision received April 18, 1997.
