Suppressors of Bir1p (Survivin) Identify Roles for the Chromosomal Passenger Protein Pic1p (INCENP) and the Replication Initiation Factor Psf2p in Chromosome Segregation

Abstract

Fission yeast Bir1p/Cut17p/Pbh1p, the homolog of human Survivin, is a conserved chromosomal passenger protein that is required for cell division and cytokinesis. To study how Bir1p promotes accurate segregation of chromosomes, we generated and analyzed a temperature-sensitive allele, bir1-46, and carried out genetic screens to find genes that interact with bir1⁺. We identified Psf2p, a component of the GINS complex required for DNA replication initiation, as a high-copy-number suppressor of the bir1-46 growth defect. Loss of Psf2p function by depletion or deletion or by use of a temperature-sensitive allele, psf2-209, resulted in chromosome missegregation that was associated with mislocalization of Bir1p. We also found that the human homolog of Psf2p, PSF2, was required for proper chromosome segregation. In addition, we observed that high-copy-number expression of Pic1p, the fission yeast homolog of INCENP (inner centromere protein), suppressed bir1-46. Pic1p exhibited a localization pattern typical of chromosomal passenger proteins. Deletion of pic1⁺ caused chromosome missegregation phenotypes similar to those of bir1-46. Our data suggest that Bir1p and Pic1p act as part of a conserved chromosomal passenger complex and that Psf2p/GINS indirectly affects the localization and function of this complex in chromosome segregation, perhaps through an S-phase role in centromere replication.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://mcb.asm.org/.

ACKNOWLEDGMENTS

We thank Don Cleveland, Nicholas Hastie, Geoff Wahl, and Mitsuhiro Yanagida for generous gifts of strains, cell lines, and antibodies, and Arshad Desai and Susan Gasser for communicating results prior to publication. We thank Walter Eckhart for encouragement and Jill Meisenhelder and Suzanne Simon for assistance. We are especially grateful to Larn Hwang for help with siRNA experiments. We thank Beth Baber and Huaiyu Sun for comments on the manuscript.

H.-K.H. was supported by fellowship DRG-1531 from the Damon Runyon Cancer Research Foundation. J.M.B. was supported by the Damon Runyon Cancer Research Foundation (DRG-1634) and the National Institutes of Health (CA009370). J.D.L. was supported by the American Cancer Society (PF9922801CCG). S.L.F. was a Stohlman Scholar of the Leukemia and Lymphoma Society. T.H. is a Frank and Else Schilling American Cancer Society Research Professor. This work was supported by Public Health Service grants CA14195, CA39780, and CA80100 from the National Cancer Institute (T.H.) and by GM059321 from the National Institutes of General Medicine and MCB 9974732 from the National Science Foundation (S.L.F.).