Abstract
SUMO proteins are small ubiquitin-like modifiers found in all eukaryotes that become covalently conjugated to other cellular proteins. The SUMO conjugation pathway is biochemically similar to ubiquitin conjugation, although the enzymes within the pathway act exclusively on SUMO proteins. This post-translational modification controls many processes. Here, I will focus on evidence that SUMOylation plays a critical role(s) in mitosis: Early studies showed a genetic requirement for SUMO pathway components in the process of cell division, while later findings implicated SUMOylation in the control of mitotic chromosome structure, cell cycle progression, kinetochore function and cytokinesis. Recent insights into the targets of SUMOylation are likely to be extremely helpful in understanding each of these aspects. Finally, growing evidence suggests that SUMOylation is a downstream target of regulation through Ran, a small GTPase with important functions in both interphase nuclear trafficking and mitotic spindle assembly.
Highlights
SUMO proteins are small ubiquitin-like modifiers that become covalently conjugated to cellular proteins
I will focus on evidence that SUMOylation plays a critical role in mitotic chromosome structure and segregation, and on how this pathway may be regulated during mitosis
Overexpression of Siz1p significantly enhances the sensitivity of ts pds5 strains. Consistent with these results, increased Ulp2p levels decrease Pds5p SUMOylation, while elevated Siz1p enhances Pds5p modification. These findings suggest that Pds5p interacts with the Cohesin complex to increase the strength of sister chromatid cohesion, and Within the Condensin complex, Smc2p and Smc4p associate with non-Structural Maintenance of Chromosomes (SMC) subunits Ycs4p, Ycs5p and Brn1p
Summary
SUMO proteins are small ubiquitin-like modifiers that become covalently conjugated to cellular proteins. Matunis and colleagues have recently shown that suppression of mitotic SUMOylation in HeLa cells by overexpression of SENP2 leads to a chromosome segregation defect through disruption of CENP-E targeting to kinetochores [81] They further observed CENP-E itself is both a SUMO2/3 substrate and polySUMO2/3 binding protein. Despite the stability of such interactions, they must be remodelled at the end of mitosis to allow Ulp1p-mediated deconjugation of cytoplasmic substrates, Septins It appears that these two karopherins have a complex and perhaps antagonistic roles in this process [89]: Ulp1p mutants that cannot bind Importin-α/β target aberrantly to the Septin ring in large budded cells, suggesting that Importin-α/β normally antagonizes recruitment of Ulp to the bud neck. Mechanisms that may underlie the specificity of PIASy recruitment will obviously be important topics for further investigation
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