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Molecular and Cellular Biology, February 2004, p. 1070-1080, Vol. 24, No. 3
0270-7306/04/$08.00+0     DOI: 10.1128/MCB.24.3.1070-1080.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Novel Isotypic {gamma}/{zeta} Subunits Reveal Three Coatomer Complexes in Mammals

Dominik Wegmann,{dagger} Pablo Hess,{dagger} Carola Baier,{ddagger} Felix T. Wieland,* and Constanze Reinhard*

Biochemie-Zentrum Heidelberg, 69120 Heidelberg, Germany

Received 25 July 2003/ Returned for modification 30 September 2003/ Accepted 28 October 2003

In early secretory transport, coat recruitment for the formation of coat protein I (COPI) vesicles involves binding to donor Golgi membranes of the small GTPase ADP-ribosylation factor 1 and subsequent attachment of the cytoplasmic heptameric complex coatomer. Various hypotheses exist as to the precise role of and possible routes taken by COPI vesicles in the mammalian cell. Here we report the ubiquitous expression of two novel isotypes of coatomer subunits {gamma}- and {zeta}-COP that are incorporated into coatomer, and show that three isotypes exist of the complex defined by the subunit combinations {gamma}1/{zeta}1, {gamma}1/{zeta}2, and {gamma}2/{zeta}1. In a liver cytosol, these forms make up the total coatomer in a ratio of about 2:1:2, respectively. The coatomer isotypes are located differentially within the early secretory pathway, and the {gamma}2/{zeta}1 isotype is preferentially incorporated into COPI vesicles. A population of COPI vesicles was characterized that almost exclusively contains {gamma}2/{zeta}1 coatomer. This existence of three structurally different forms of coatomer will need to be considered in future models of COPI-mediated transport.

* Corresponding author. Mailing address: Biochemie-Zentrum Heidelberg (BZH), Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 328, 69120 Heidelberg, Germany. Phone for Felix T. Wieland: 49 6221 54 4150. Fax: 49 6221 54 4366. E-mail: felix.wieland{at}urz.uni-heidelberg.de. Phone for Constanze Reinhard: 49 6221 54 5420. Fax: 49 6221 54 4366. E-mail: constanze.reinhard{at}bzh.uni-heidelberg.de.

{dagger} D.W. and P.H. contributed equally to this work.

{ddagger} Present address: Max-Planck-Institut für Biochemie, 82152 Martinsried, Germany.

Molecular and Cellular Biology, February 2004, p. 1070-1080, Vol. 24, No. 3
0022-538X/04/$08.00+0     DOI: 10.1128/MCB.24.3.1070-1080.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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