Num1p Interaction with SUMO

During cell division, the daughter centrosome is pulled to the centre of the bud cortex by Num1 dynein-dynactin. Num1 is a protein that works as a cortical anchor for the dynein motor, transporting the nucleus from the mother cell to the bud. Num1 is not essential for nuclear migration, but it is important for efficiency. It is suspected that the Num1 protein is sumoylated. Sumoylation is the post- translational modification of proteins by Small Ubiquitin like modifiers (SUMO). SUMO proteins regulate various cellular processes including nuclear transport, transcription, chromosome segregation, and DNA repair. Sumoylation can affect the stability, localization, or activity of a protein. A two-hybrid assay will be used to test for the interaction of Num1 with SMT3, the SUMO homologue in yeast. A temperature sensitive strain of Ubiquitin- Like Protein-1 (Ulp1), that inactivates the protease activity of Ulp1p at 37°C and cleaves Smt3p from any proteins conjugated to it, will be used to identify whether Num1p is sumoylated. The localization and activity of Num1p is important because of this protein’s role in the nuclear migration and placement of the bud. These findings will lead to a better understanding of how Num1p functions and interacts with other proteins.