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. 1999 Nov 9;96(23):13208-13.
doi: 10.1073/pnas.96.23.13208.

Participation of Bir1p, a member of the inhibitor of apoptosis family, in yeast chromosome segregation events

H J Yoon  1 , J Carbon
Affiliations

Participation of Bir1p, a member of the inhibitor of apoptosis family, in yeast chromosome segregation events

H J Yoon et al. Proc Natl Acad Sci U S A. .

Abstract

Yeast two-hybrid and genetic interaction screens indicate that Bir1p, a yeast protein containing phylogenetically conserved antiapoptotic repeat domains called baculovirus inhibitor of apoptosis repeats (BIRs), is involved in chromosome segregation events. In the two-hybrid screen, Bir1p specifically interacts with Ndc10p, an essential component of the yeast kinetochore. Although Bir1p carries two BIR motifs in the N-terminal region, the C-terminal third of the protein is sufficient to provide strong interaction with Ndc10p and moderate interaction with Skp1p, another essential component of the yeast kinetochore. In addition, deletion of BIR1 is synthetically lethal with deletion of CBF1 or CTF19, genes specifying two other components of the yeast kinetochore. Yeast cells deleted of BIR1 have a chromosome-loss phenotype, which can be completely rescued by elevating NDC10 dosage. Furthermore, overexpression of either full-length or the C-terminal region of Bir1p can efficiently suppress the chromosome-loss phenotype of both bir1Delta null and skp1-4 mutants. Our data suggest that Bir1p participates in chromosome segregation events, either directly or via interaction with kinetochore proteins, and these effects are apparently not mediated by the BIR domains of Bir1p.

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Figures

Figure 1
Figure 1
In vivo binding of Bir1p to Ndc10p. (A) Two-hybrid interaction between a Bir1p fragment and known kinetochore proteins. A tester strain PJ69–4A (17) carrying the plasmid pACD-Bir1 (C332) was transformed with various plasmids that express DBD alone or DBD-fused Ndc10p, Cep3p, Ctf13p, Skp1p, or Cbf1p. The transformants were streaked on SD/His− medium containing 2 mM 3-AT (3-amino-1 2,4-triazole) to test expression of the HIS3 reporter gene. (B) Two-hybrid assay with strain PJ69-4A carrying pDBD-Bir1 (full). Strain PJ69-4A/pDBD-Bir1 (full) bearing plasmids expressing ACD-fused Mif2p, Cse4p, Ctf19p, Mcm21p, Okp1p, or Slk19p did not grow on minimal salt-dextrose/His− medium containing 2 mM 3-AT (not shown). (C) Identification of Bir1p regions interacting with Ndc10p. (Top) Schematic view of Bir1p showing the relative locations of BIR domains 1 (R1), 2 (R2), and of nuclear localization signal (NLS), a bipartite nuclear localization signal. Various truncated Bir1p fragments as shown here (See Materials and Methods) were tested for two-hybrid interactions with Ndc10p on SD/His− medium containing 2 mM 3-AT.
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