Date of Award
Master of Science (MS)
Cancer and Developmental Biology
Richard Kriwacki, Ph.D.
Tanja Mittag, Ph.D. Brenda Schulman, Ph.D. Susan Senogles, Ph.D. J. Paul Taylor, M.D., Ph.D.
Membrane-less organelle, Nucleolus, Phase Separation, Structural Biology
Nucleoli are nuclear membrane-less organelles that are the sites for ribosome biogenesis and serve as sensors of cellular stress. Weak, multivalent protein-protein interactions and interactions between disordered, low complexity domains (LCDs) and rRNA have been shown to promote liquid-liquid phase separation (LLPS) in vitro, suggesting a basis for the liquid-like behavior of nucleoli. Nucleophosmin (NPM1), a multifunctional and highly abundant nucleolar protein, exhibits structural features associated with LLPS suggesting a role in nucleolar organization. Specifically, NPM1 forms a pentamer through its N-terminal oligomerization domain and can bind to rRNA through its C-terminal nucleic acid binding domain. Multiple acidic tracts throughout NPM1, two within an intrinsically disordered region (IDR), confer additional multivalency and mediate interactions with proteins that contain multiple arginine-rich motifs (R-proteins). Using a variety of techniques, we have identified several nucleolar R-proteins which bind to and phase separate with NPM1. Here we show that the liquid-like properties of NPM1 droplets can be tuned by modulating the extent of electrostatic interactions within the droplet. We propose that a hierarchy of R-motifs, varying in valency and affinity, within nucleolar R-proteins exists which leads to a heterogeneous network of interactions between proteins and rRNA within nucleoli, thus promoting formation of a dynamic liquid-like phase conducive to ribosome biogenesis and other nucleolar functions.
Cika, Jaclyn Alicia (http://orcid.org/0000-0003-2911-5648), "The Nucleolar Protein Nucleophosmin Undergoes Liquid-Liquid Phase Separation with Arginine-Rich Nucleolar Proteins through Weak, Multivalent Electrostatic Interactions" (2016). Theses and Dissertations (ETD). Paper 411. http://dx.doi.org/10.21007/etd.cghs.2016.0414.