Date of Award
2025
Document Type
Honors Thesis (Colby Access Only)
Department
Colby College. Biology Dept.
Advisor(s)
Yee Mon Thu
Abstract
DNA replication errors threaten genome integrity and can result in mutations and oncogenic transformation. To prevent such outcomes, eukaryotic cells employ multiple surveillance mechanisms, including the S-phase checkpoint and the spindle assembly checkpoint (SAC), to coordinate DNA replication with mitotic progression. The Chromosomal Passenger Complex (CPC), particularly the conserved subunit Bir1 (Survivin in humans), plays a critical role in SAC function by ensuring proper kinetochore-microtubule attachments. Recent evidence suggests that post-translational modifications such as sumoylation regulate CPC localization and activity. However, the precise role of Bir1 sumoylation during replication stress remains unclear. We hypothesized that Bir1 sumoylation is essential for maintaining SAC-dependent G2/M arrest in the presence of DNA damage. To test this, we used a Saccharomyces cerevisiae strain expressing a BIR1-SuOff mutant, in which SUMO isopeptidase activity (Ulp1) is fused to Bir1 to prevent its sumoylation, alongside a catalytically inactive control (BIR1-SuC). Upon treatment with methyl methanesulfonate (MMS) to induce replication stress, preliminary data using flow cytometry revealed that BIR1-SuOff cells accumulated less in G2/M, unlike control cells, indicating premature mitotic entry. These findings support the conclusion that Bir1 sumoylation is required for proper SAC activation and mitotic arrest under replication stress, highlighting a critical regulatory mechanism that coordinates DNA replication with chromosome segregation.
Keywords
Sumoylation, Spindle Assembly Checkpoint, cell cycle, DNA damage
Recommended Citation
Baadi, Nkechi, "The Impacts of Bir1 Sumoylation on the Spindle Assembly Checkpoint under Replication Stress Conditions" (2025). Honors Theses. Paper 1508.https://digitalcommons.colby.edu/honorstheses/1508