A new role for kinesin-directed transport of Bik1p (CLIP-170) in Saccharomyces cerevisiae

Abstract

Bik1p is the budding yeast counterpart of the CLIP-170 family of microtubule plus-end tracking proteins, which are required for dynein localization at plus ends and dynein-dependent spindle positioning. CLIP-170 proteins make up a CAP-Gly microtubule-binding domain, which sustains their microtubule plus-end tracking behaviour. However, in yeast, Bik1p travels towards plus ends as a cargo of the plus-end-directed kinesin Kip2p. Additionally, Kip2p behaves as a plus-end-tracking protein; hence, it has been proposed that Bik1p might track plus ends principally as a cargo of Kip2p. Here, we examined Bik1p localization in yeast strains expressing mutant tubulin lacking the C-terminal amino acid (Glu tubulin; lacking Phe), the interaction of which with Bik1p is severely impaired compared with wild type. In Glu-tubulin strains, despite the presence of robust Kip2p comets at microtubule plus ends, Bik1p failed to track plus ends. Despite Bik1p depletion at plus ends, dynein positioning at the same plus ends was unperturbed. Video microscopy and genetic evidence indicated that dynein was transported at plus ends in a Kip2p-Bik1p-dependent manner, and was then capable of tracking Bik1p-depleted plus ends. These results indicate that Bik1p interactions with tubulin are important for Bik1p plus-end tracking, and suggest alternative pathways for Bik1p-Kip2p-dependent dynein localization at plus ends.

Mechanism of Nuclear Movements in a Multinucleated Cell

“…The catastrophe rate was then calculated as v g /L, which, compared with wild type, increased about fourfold in the bik1 mutant and decreased about twofold in the kip3 mutant ( Figure 4B). The catastrophe rates for S. cerevisiae and A. gossypii cMTs are similar, but the growth and shrinkage speeds are threefold slower in S. cerevisiae ( Figure 4B) according to averaged published data (Tirnauer et al, 1999;Adames and Cooper, 2000;Kosco et al, 2001;Huang and Huffaker, 2006;Wolyniak et al, 2006;Caudron et al, 2008).…”

CAP-Gly proteins contribute to microtubule-dependent trafficking via interactions with the C-terminal aromatic residue of α-tubulin

“…Indeed, Nip100 interacts with Snx4, Imh1, Tlg1, Vps20, and Vps60, which are known to be involved in trafficking between endosomes and late Golgi or late Golgi and the vacuole. Notably, and in striking contrast to Bik1 and Nip100, the Cend-tracking protein Bim1, the yeast EB1 ortholog, which is insensitive to the tyrosination status of microtubules, 22,23,32 has not been reported to interact with endosomal proteins. In line with this difference in interaction partners, BIM1 deletion caused no alterations to Snc1 distribution.…”

“…[40][41][42] In addition, in yeast, Bik1 is actively transported to the microtubule Cends by the kinesin Kip2, which facilitates its targeted localization. 32,43 Recently, Kip2 phosphorylation by the yeast kinase GSK3b was demonstrated to tune its association with microtubules. 44 A simple hypothesis is that Rho1 modulates Bik1s association with microtubules through the recruitment of specific kinase(s)/phosphatase(s) which control Bik1 phosphorylation or the phosphorylation state of other partners in its interaction with microtubules.…”

“…44 A simple hypothesis is that Rho1 modulates Bik1s association with microtubules through the recruitment of specific kinase(s)/phosphatase(s) which control Bik1 phosphorylation or the phosphorylation state of other partners in its interaction with microtubules. The Cend-tracking protein Bim1 is known to contribute to Bik1 Cend localization in the tub1-Glu strain, 32 but whether Rho1 affects Bim1 localization at microtubule Cends or its interaction with Bik1 has yet to be investigated. 32,45,46 Rho1 has been demonstrated to interact with Nip100 47 ( Table 1), suggesting that it might regulate this CAP-Gly protein.…”

“…The Cend-tracking protein Bim1 is known to contribute to Bik1 Cend localization in the tub1-Glu strain, 32 but whether Rho1 affects Bim1 localization at microtubule Cends or its interaction with Bik1 has yet to be investigated. 32,45,46 Rho1 has been demonstrated to interact with Nip100 47 ( Table 1), suggesting that it might regulate this CAP-Gly protein. A detailed analysis of Rho1s contribution to the recruitment and affinity of all microtubule Cend-tracking proteins will need to be performed to gain a more comprehensive view of the role played by this GTPase on CTips proteins and a possible specificity in the regulation of CAP-Gly proteins.…”