The export of membrane proteins along the secretory pathway is initiated at the endoplasmic reticulum after proteins are folded and packaged inside this organelle by their recruiting into the coat complex COPII vesicles. It is proposed that cargo receptors are required for the correct transport of proteins to its target membrane, however, little is known about ER export signals for cargo receptors. Erv14/Cornichon belong to a well conserved protein family in Eukaryotes, and have been proposed to function as cargo receptors for many transmembrane proteins. Amino acid sequence alignment showed the presence of a conserved acidic motif in the C-terminal in homologues from plants and yeast. Here, we demonstrate that mutation of the C-terminal acidic motif from ScErv14 or OsCNIH1, did not alter the localization of these cargo receptors, however it modified the proper targeting of the plasma membrane transporters Nha1p, Pdr12p and Qdr2p. Our results suggest that mistargeting of these plasma membrane proteins is a consequence of a weaker interaction between the cargo receptor and cargo proteins caused by the mutation of the C-terminal acidic motif.

Department of Membrane Transport Institute of Physiology The Czech Academy of Sciences 142 20 Prague 4 Czech Republic

Instituto de Biotecnología Universidad Nacional Autónoma de México Apdo Postal 510 3 Cuernavaca Morelos 62250 México

Instituto de Biotecnología Universidad Nacional Autónoma de México Apdo Postal 510 3 Cuernavaca Morelos 62250 México; Instituto de Investigación en Ciencias Básicas y Aplicadas Universidad Autónoma del Estado de Morelos Av Universidad 1001 Col Chamilpa Cuernavaca Morelos 62210 México

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The Role of Cornichons in the Biogenesis and Functioning of Monovalent-Cation Transport Systems