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© The Rockefeller University Press,
0021-9525/1997//1063 $5.00
The Journal of Cell Biology, Volume 139, Number 5,
, 1997 1063-1076
Article |
KAR5 Encodes a Novel Pheromone-inducible Protein Required for Homotypic Nuclear Fusion
KAR5 is required for membrane fusion during karyogamy, the process of nuclear fusion during yeast mating. To investigate the molecular mechanism of nuclear fusion, we cloned and characterized the KAR5 gene and its product. KAR5 is a nonessential gene, and deletion mutations produce a bilateral defect in the homotypic fusion of yeast nuclei. KAR5 encodes a novel protein that shares similarity with a protein in Schizosaccharomyces pombe that may play a similar role in nuclear fusion. Kar5p is induced as part of the pheromone response pathway, suggesting that this protein uniquely plays a specific role during mating in nuclear membrane fusion. Kar5p is a membrane protein with its soluble domain entirely contained within the lumen of the endoplasmic reticulum. In pheromone-treated cells, Kar5p was localized to the vicinity of the spindle pole body, the initial site of fusion between haploid nuclei during karyogamy. We propose that Kar5p is required for the completion of nuclear membrane fusion and may play a role in the organization of the membrane fusion complex.
Abbreviations used in this paper: DAPI, 4',6-diamidino-2-phenylindole; GST, glutathione-S-transferase; PRE, pheromone response element; SC, synthetic complete; SPB, spindle pole body.
Thanks to Jasper Rine, Sue Biggins, and Nancy Hawkins for critical reading of this manuscript and to Jim Broach, Gerry Waters, Scott Ederman, Mike Snyder, and Martin Latterich for reagents, useful comments, and communicating unpublished results. We also thank Don Huddler and especially Laurie Jo Kurihara for invaluable suggestions and comments.
This research was supported by a National Institutes of Health (NIH) grant (GM37739) to M.D. Rose. C.T. Beh and V. Brizzio were partially supported by institutional NIH Genetics and Cell and Molecular Biology Training grants.
Address all correspondence to Mark D. Rose, Department of Molecular Biology, Princeton University, Princeton, NJ 08544-1014. Tel.: (609) 258-2804. Fax: (609) 258-6175. E-mail: mrose{at}watson.princeton.edu
Christopher Beh's current address is Department of Molecular and Cellular Biology, 401 Barker Hall, University of California, Berkeley, CA 94720.
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