title: Dysregulated Arl1, a regulator of post-Golgi vesicle tethering, can inhibit endosomal transport and cell proliferation in yeast.
abstract: Small monomeric G proteins regulated in part by GTPase-activating proteins (GAPs) are molecular switches for several aspects of vesicular transport. The yeast Gcs1 protein is a dual-specificity GAP for ADP-ribosylation factor (Arf) and Arf-like (Arl)1 G proteins, and also has GAP-independent activities. The absence of Gcs1 imposes cold sensitivity for growth and endosomal transport; here we present evidence that dysregulated Arl1 may cause these impairments. We show that gene deletions affecting the Arl1 or Ypt6 vesicle-tethering pathways prevent Arl1 activation and membrane localization, and restore growth and trafficking in the absence of Gcs1. A mutant version of Gcs1 deficient for both ArfGAP and Arl1GAP activity in vitro still allows growth and endosomal transport, suggesting that the function of Gcs1 that is required for these processes is independent of GAP activity. We propose that, in the absence of this GAP-independent regulation by Gcs1, the resulting dysregulated Arl1 prevents growth and impairs endosomal transport at low temperatures. In cells with dysregulated Arl1, an increased abundance of the Arl1 effector Imh1 restores growth and trafficking, and does so through Arl1 binding. Protein sequestration at the trans-Golgi membrane by dysregulated, active Arl1 may therefore be the mechanism of inhibition.
authors.affiliation: Department of Microbiology & Immunology, Dalhousie University, Halifax, Nova Scotia, Canada B3H 1X5.
authors.forename: Jeremy J R
authors.initials: JJ
authors.lastname: Benjamin
authors.forename: Pak P
authors.initials: PP
authors.lastname: Poon
authors.forename: John D
authors.initials: JD
authors.lastname: Drysdale
authors.forename: Xiangmin
authors.initials: X
authors.lastname: Wang
authors.forename: Richard A
authors.initials: RA
authors.lastname: Singer
authors.forename: Gerald C
authors.initials: GC
authors.lastname: Johnston
mesh_terms: D020727:ADP-Ribosylation Factors / Q000378:metabolism; D051046:Amino-Acid N-Acetyltransferase / Q000378:metabolism; D003080:Cold Temperature; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004705:Endocytosis / Q000502:physiology; D019204:GTP-Binding Proteins / Q000378:metabolism; D020690:GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism; D006056:Golgi Apparatus / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D057146:Multivesicular Bodies / Q000378:metabolism*; D063211:N-Terminal Acetyltransferase C; D011485:Protein Binding; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism*; D021601:trans-Golgi Network / Q000235:genetics / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; C089147:GCS1 protein, S cerevisiae; D020690:GTPase-Activating Proteins; C117417:IMH1 protein, S cerevisiae; D008565:Membrane Proteins; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; D051046:Amino-Acid N-Acetyltransferase; C528042:MAK31 protein, S cerevisiae; D063211:N-Terminal Acetyltransferase C; C487039:ARL1 protein, S cerevisiae; D019204:GTP-Binding Proteins; D020727:ADP-Ribosylation Factors; D020559:Monomeric GTP-Binding Proteins; C499307:YPT6 protein, S cerevisiae