title: Sec23 homolog Nel1 is a novel GTPase-activating protein for Sar1 but does not function as a subunit of the coat protein complex II (COPII) coat.
abstract: The coat protein complex II (COPII) generates transport carriers from the endoplasmic reticulum (ER) under the control of the small GTPase Sar1. Sec23 is well known as a structural component of the COPII coat and as a GTPase-activating protein (GAP) for Sar1. Here, we showed that Saccharomyces cerevisiae contains a novel Sec23 paralog, Nel1, which appears not to function as a subunit of the COPII coat. Nel1 does not associate with any of the COPII components, but it exhibits strong Sar1 GAP activity. We also demonstrated that the chromosomal deletion of NEL1 leads to a significant growth defect in the temperature-sensitive sar1D32G background, suggesting a possible functional link between these proteins. In contrast to Sec23, which is predominantly localized at ER exit sites on the ER membrane, a major proportion of Nel1 is localized throughout the cytosol. Our findings highlight a possible role of Nel1 as a novel GAP for Sar1.
authors.affiliation: From the Department of Biological Sciences, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033 and.
authors.forename: Chie
authors.initials: C
authors.lastname: Kodera
authors.affiliation: the Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8902, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Yorimitsu
authors.affiliation: From the Department of Biological Sciences, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033 and the Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8902, Japan kensato@bio.c.u-tokyo.ac.jp.
authors.forename: Ken
authors.initials: K
authors.lastname: Sato
mesh_terms: D000595:Amino Acid Sequence; D022181:COP-Coated Vesicles; D015825:Chromosomes, Fungal; D020690:GTPase-Activating Proteins / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000378:metabolism*
chemical_list: D020690:GTPase-Activating Proteins; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; D020559:Monomeric GTP-Binding Proteins; C077395:SAR1 protein, S cerevisiae
keywords: Endoplasmic Reticulum (ER); Membrane Trafficking; Small GTPase; Vesicles; Yeast