Functional and physical interactions between partial molecules of STE6, a yeast ATP-binding cassette protein.
The Saccharomyces cerevisiae a-factor transporter, STE6, is a member of the ATP binding cassette (ABC) transporter superfamily. ABC proteins consist of four modular units that comprise two membrane-spanning domains (MSDs) and two nucleotide-binding domains (NBDs). Like many ABC proteins, STE6 contains these four domains in a single polypeptide; certain other ABC proteins are encoded as pairs of "half-molecules" or are further subdivided. Our previous studies demonstrated that STE6 can be expressed as two half-molecules that are functional when co-expressed. Here we dissect the interactions between modules of STE6 in greater detail. We show by co-immunoprecipitation that STE6 half-molecules interact physically, supporting the view that they co-assemble in vivo to form a functional transporter. We also demonstrate a physical interaction between a STE6 half-molecule and full-length STE6; such complexes appear to be functional, based on the striking finding that the defective activity of full-length STE6 mutated in one of its NBDs can be corrected by co-expression of the corresponding "wild-type" half-molecule. We also show that a quarter-molecule consisting solely of the N-terminal MSD of STE6 can interact physically and functionally with a C-terminal three-quarter molecule of STE6, indicating that information directing the assembly of STE6 from partial molecules is contained, at least in part, within its membrane spans.
Berkower
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Department of Cell Biology and Anatomy, The Johns Hopkins School of Medicine, Baltimore, Maryland 21205, USA.
Taglicht
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Michaelis
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D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D002451:Cell Compartmentation; D003433:Crosses, Genetic; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D006023:Glycoproteins; D008954:Models, Biological; D009154:Mutation; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism*; D011233:Precipitin Tests; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D013329:Structure-Activity Relationship
D018528:ATP-Binding Cassette Transporters; D005656:Fungal Proteins; D006023:Glycoproteins; D010446:Peptide Fragments; D011994:Recombinant Proteins; C489277:STE6 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins