Ran-binding Protein-1 Is an Essential Component of the Ran/RCC1 Molecular Switch System in Budding Yeast

doi:10.1074/jbc.270.5.1975

Ran-binding Protein-1 Is an Essential Component of the Ran/RCC1 Molecular Switch System in Budding Yeast (*)

From the (1)Departments of Cell Biology,
(2)Biochemistry,
(3)Institute for Molecular Genetics, and
(4)Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas 77030

^§ To whom correspondence should be addressed:
Dept. of Cell Biology, 126A, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030.
Tel.: 713-798-5295; Fax: 713-790-0545; ILIAO{at}MBCR.BCM.TMC.EDU

Abstract

We have performed a screen for genes that affect chromosome stability when overexpressed in the budding yeast Saccharomyces cerevisiae. Two of the genes recovered in the screen, CST17 and CST20, share a number of phenotypic properties, suggesting their involvement in the same cellular process. DNA sequence analysis of these genes revealed that they encode components of the Ran/RCC1 molecular switch system: CST17 is Ran itself (Ras-like nuclear protein) and CST20 is a novel yeast protein with a high degree of similarity to mammalian RanBP1, which is known to interact with Ran-GTP in vitro. We demonstrate that the CST20 protein can interact with Ran-GTP in vitro under similar conditions, indicating that it is the functional yeast homolog of mammalian RanBP1. The results of immunoprecipitation experiments show that the two yeast proteins form a complex in vivo. Deletion of the gene encoding RanBP1 revealed that it is essential for viability, as are Ran and RCC1. Similar phenotypic consequences of overproduction of either Ran or RanBP1 indicate that the latter protein is a functional component of the Ran/RCC1 molecular switch system, which is implicated in the control of a number of nuclear functions. Our finding that overproduction of two components of this system results in mitotic chromosome nondisjunction and sensitivity to an anti-microtubule drug benomyl suggest their involvement in mitosis as well. Thus RanBP1 is a functional component of a highly conserved molecular system that affects diverse cellular processes. The availability of this gene in S. cerevisiae provides a genetic system for the analysis of RanBP1 function in vivo.

Footnotes

↵^¶ Pew Scholar in the Biomedical Sciences and an Investigator of the Howard Hughes Medical Institute.
↵* This work was supported by National Institutes of Health Grants CA41424 (to B. R. B.), GM49119 (to S. S.), and GM44664 (to S. J. E.), National Institutes of Health Predoctoral Training Grant AG00183 (to U. W. M.), and by Robert Welch Foundation Grant Q-1226 (to S. S.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹Demeter, J., Morphew, M., and Sazer, S.(1995) Proc. Natl. Acad. Sci. U. S. A., in press.
↵² The abbreviations used are:

CF

chromosome fragment

bp

base pair(s)

kb

kilobase pair(s)

HA

an epitope of influenza virus hemagglutinin

HU

hydroxyurea.
↵³Accession number X65925 (H. Holtzer, unpublished data).
↵⁴X. He and S. Sazer, unpublished data.
↵⁵F. R. Bischoff and H. Ponstingl, personal communication.
- Received November 23, 1994.