Talk abstracts
Talk on Friday 02:00-02:15pm submitted by Amber LaPeruta
Not just a phase: understanding ribosome biogenesis using liquid-liquid phase biology
Amber J. LaPeruta (Carnegie Mellon University Department of Biological Sciences), Jelena Micic (Carnegie Mellon University Department of Biological Sciences), Daniel M. Wilson (Carnegie Mellon University Department of Biological Sciences), Fiona Fitzgerald (Carnegie Mellon University Department of Biological Sciences), John L. Woolford Jr. (Carnegie Mellon University Department of Biological Sciences)
Abstract:
The ribosome is an extremely complex structure composed of 79 ribosomal proteins (RPs) and 4 ribosomal RNAs (rRNAs) (25S, 18S, 5.8S and 5S), and is synthesized with the assistance of >200 assembly factors (AFs). The initial stages of ribosome biogenesis take place in the nucleolus, a membraneless organelle within the nucleus that is assembled via liquid-liquid phase separation. The interrelation between ribosome assembly and the nucleolus has been noted for decades. Nucleolar function in response to environmental signals regulates ribosome biogenesis, and inhibition of or defects in ribosome biogenesis alter nucleolar structure. This raises numerous questions. How does a nucleolus form as ribosomes assemble? What qualities of pre-ribosomes retain them in the nucleolus, and what changes must occur in order for them to be released? To answer these questions, we analyzed cryo-EM structures of pre-ribosomes within and outside of the nucleolus from the perspective of liquid-liquid phase biology. A major precept in phase biology is that highly valent molecules and complexes, which are capable of undergoing multiple simultaneous interactions, have greater phase separation potential. We hypothesize that the valency of pre-ribosomes decreases as they mature because the number of heterogeneous trans-interacting RNA and protein domains, which cannot be visualized by cryo-EM, decreases. To explore these ideas, we determined the abundance of predicted trans-interacting RNA and protein structures not accounted for in the cryo-EM structures of nascent large ribosomal subunits undergoing nucleolar and non-nucleolar stages of assembly. Using these data, we have identified qualities of pre-ribosomes that support nucleolar retention. Furthermore, we created a general model for how rRNA, RPs, and AFs function during ribosome biogenesis to ultimately decrease the valency of pre-ribosomes and facilitate their release from the nucleolus.
Keywords: ribosome, nucleolus, liquid-liquid phase