Saccharomyces cerevisiae Rab-GDI displacement factor ortholog Yip3p forms distinct complexes with the Ypt1 Rab GTPase and the reticulon Rtn1p.
Rab GTPases are crucial regulators of organelle biogenesis, maintenance, and transport. Multiple Rabs are expressed in all cells, and each is localized to a distinct set of organelles, but little is known regarding the mechanisms by which Rabs are targeted to their resident organelles. Integral membrane proteins have been postulated to serve as receptors that recruit Rabs from the cytosol in a complex with the Rab chaperone, GDI, to facilitate the dissociation of Rab and GDI, hence facilitating loading of Rabs on membranes. We show here that the yeast (Saccharomyces cerevisiae) Golgi Rab GTPase Ypt1p can be copurified with the integral membrane protein Yip3p from detergent cell extracts. In addition, a member of the highly conserved reticulon protein family, Rtn1p, is also associated with Yip3p in vivo. However, Ypt1p did not copurify with Rtn1p, indicating that Yip3p is a component of at least two different protein complexes. Yip3p and Rtn1p are only partially colocalized in cells, with Yip3p localized predominantly to the Golgi and secondarily to the endoplasmic reticulum, whereas Rtn1p is localized predominantly to the endoplasmic reticulum and secondarily to the Golgi. Surprisingly, the intracellular localization of Rabs was not perturbed in yip3Delta or rtn1Delta mutants, suggesting that these proteins do not play a role in targeting Rabs to intracellular membranes. These data indicate that Yip3p may have multiple functions and that its interaction with Rabs is not critical for their recruitment to organelle membranes.
Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, 421 Curie Blvd. BRB 2/3 Room 1010, Philadelphia, PA 19104-6058, USA.
Jinming
J
Geng
Marcus E
ME
Shin
Penney M
PM
Gilbert
Ruth N
RN
Collins
Christopher G
CG
Burd
D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism; D006056:Golgi Apparatus / Q000235:genetics / Q000378:metabolism; D020730:Guanine Nucleotide Dissociation Inhibitors / Q000378:metabolism*; D046911:Macromolecular Substances / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
C086796:GDP dissociation inhibitor 1; D020730:Guanine Nucleotide Dissociation Inhibitors; D046911:Macromolecular Substances; C505725:Rtn1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; C505724:Yip3 protein, S cerevisiae; C060755:YPT1 protein, S cerevisiae; D020691:rab GTP-Binding Proteins