Cut1 is loaded onto the spindle by binding to Cut2 and promotes anaphase spindle movement upon Cut2 proteolysis

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• The Cut1 and Cut2 proteins in *Schizosaccharomyces pombe* form a complex essential for sister chromatid separation during anaphase.
• Degradation of polyubiquitinated Cut2 at anaphase onset, regulated by the anaphase-promoting complex/cyclosome, is critical for this process.
• Non-degradable Cut2 inhibits sister chromatid separation and spindle elongation, highlighting the importance of its regulated degradation.

Purpose of the Study:

• To investigate the role of the Cut1-Cut2 protein interaction in the process of sister chromatid separation.
• To understand how the interaction between Cut1 and Cut2 influences cell cycle progression and spindle dynamics.

Main Methods:

• Analysis of temperature-sensitive Cut2 mutants with substitutions in the carboxyl terminus affecting Cut1 interaction.
• Cell cycle-based localization studies of Cut1 protein using microscopy.
• Investigation of Cut1-Cut2 complex formation and its impact on Cut1 localization to spindle structures.

Main Results:

• The carboxyl terminus of Cut2 interacts with the amino terminus of Cut1; mutations disrupting this interaction lead to aberrant anaphase.
• Cut1 protein is localized to the cytoplasm during interphase and translocates to spindle pole bodies and the spindle during prophase.
• The Cut1-Cut2 complex is necessary for Cut1's spindle localization; Cut1 remains bound to the anaphase spindle, requiring its conserved carboxyl terminus.

Conclusions:

• Complex formation between Cut1 and Cut2 is essential for initiating normal anaphase in *S. pombe*.
• Cut2 facilitates the loading of Cut1 onto the spindle during prophase.
• Proteolysis of Cut2 is required for the active role of Cut1 in sister chromatid separation during anaphase.