RT Journal Article
SR Electronic
T1 Nucleolar targeting in an early-branching eukaryote suggests a general physicochemical mechanism for ribosome protein sorting
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 2021.12.20.473284
DO 10.1101/2021.12.20.473284
A1 Milad Jeilani
A1 Karen Billington
A1 Jack Daniel Sunter
A1 Samuel Dean
A1 Richard John Wheeler
YR 2021
UL http://biorxiv.org/content/early/2021/12/20/2021.12.20.473284.abstract
AB The eukaryotic cell targets proteins to the organelles in which they function, both membrane-bound (like the nucleus) and non-membrane-bound (like the nucleolus). Nucleolar targeting relies on positively charged localisation signals, and has received rejuvenated interest since the widespread recognition of liquid-liquid phase separation (LLPS) as a mechanism contributing to nucleolus formation. Here, we exploit a new genome-wide analysis of protein localisation in an early-branching eukaryote, Trypanosoma brucei, to analyse general nucleolar protein properties. T. brucei nucleolar proteins have similar properties to those in common model eukaryotes, specifically basic amino acids. Using protein truncations and addition of candidate targeting sequences to proteins, we show both homopolymer runs and distributed basic amino acids give nucleolar partition, further aided by a nuclear localisation signal (NLS). These findings are consistent with phase separation models of nucleolar formation and protein physical properties being a major contributing mechanism for eukaryotic nucleolar targeting, conserved from the last eukaryotic common ancestor. Importantly, cytoplasmic ribosome proteins in comparison to mitochondrial ribosome proteins followed the same pattern – pointing to adaptation of physicochemical properties to assist segregation.Summary Statement We show protein targeting to the nucleolus is mediated by positive charge, likely across eukaryotes, and contributes to sorting of mitochondrial from cytoplasmic ribosome proteins.Competing Interest StatementThe authors have declared no competing interest.LLPSliquid-liquid phase separationNLSnuclear localisation signalNoLSnucleolar localisation signalPol IRNA Polymerase IIDRintrinsically disordered regionmNGmNeonGreen