Date of Award

Spring 2002

Document Type

Restricted Thesis

Terms of Use

© 2002 Chia-En K. Tu. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts


Biology Department

First Advisor

Elizabeth Ann Vallen


Cytokinesis is a critical process in living organisms and is the division of one cell into two. In the budding yeast Saccharomyces cerevisiae, cytokinesis occurs through the concerted action of a contractile actomyosin ring and septum formation. Formin homology (FH) proteins are an evolutionarily conserved protein family involved in cell polarization and cytokinesis by regulating actin organization. In S. cerevisiae, there are two FH proteins, Bni1 p and Bnr1 p and both proteins share an essential function. Here we analyzed various temperature-sensitive mutants and showed that the formins together are required for the formation of the actomyosin ring at the bud neck during late anaphase/telophase of the cell cycle. At the nonpermissive temperature, bni1-151 bnr1∆ cells are large, round, multiply budded and exhibit polarized actin organization but are unable to form an actin ring. In addition, we attempted to identify Bni1p- interacting proteins by performing a multicopy suppressor screen. Several truncated alleles of BNI1 and BNR1 were isolated and it was found that they were able to complement the bni1∆ bnr1∆ double mutant. An amino-terminally truncated Bni1p-GFP did not localize normally to the bud tip or bud neck and instead remained in the nucleus throughout the cell cycle. This suggests that the essential function of Bni1p does not require that it localize to the bud tip or bud neck.