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. 2021 Feb 6;169(1):87-100.
doi: 10.1093/jb/mvaa095.

RNA-recognition motifs and glycine and arginine-rich region cooperatively regulate the nucleolar localization of nucleolin

Mitsuru Okuwaki  1   2 , Ai Saotome-Nakamura  2 , Masashi Yoshimura  1 , Shoko Saito  1   2 , Hiroko Hirawake-Mogi  1 , Takeshi Sekiya  2 , Kyosuke Nagata  2
Affiliations

RNA-recognition motifs and glycine and arginine-rich region cooperatively regulate the nucleolar localization of nucleolin

Mitsuru Okuwaki et al. J Biochem. .

Abstract

Nucleolin (NCL) is a nucleolar protein i.e. involved in the regulation of the nucleolar structure and functions, and consists of three distinct regions: the N-terminal region; the middle region, which contains four RNA-recognition motifs (RRMs); and the C-terminal glycine- and arginine-rich (GAR) region. The primary function of the RRMs and GAR is thought to be specific RNA binding. However, it is not well understood how these RNA-binding regions of NCL separately or cooperatively regulate its nucleolar localization and functions. To address this issue, we constructed mutant proteins carrying point mutations at the four RRMs individually or deletion of the C-terminal GAR region. We found that the GAR deletion and the mutations in the fourth RRM (RRM4) decreased the nucleolar localization of NCL. Biochemical analyses showed that NCL interacted directly with ribosomal RNAs (rRNAs) and G-rich oligonucleotides, and that this interaction was decreased by mutations at RRM1 and RRM4 and GAR deletion. Although GAR deletion decreased the rRNA-binding activity of NCL, the mutant was efficiently coprecipitated with rRNAs and nucleolar proteins from cell extracts. These contradictory results suggest that NCL stably localizes to the nucleoli via the interactions with rRNAs and nucleolar proteins via GAR, RRM1 and RRM4.

Keywords: G-quadruplex; RNA-recognition motif; nucleolus; rRNA; ribosome biogenesis.

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