Fig. 1: A lysine-rich IDR is present in a subset of abundant, early-acting ribosome biogenesis factors.

A Schematic representation of H/ACA and C/D snoRNPs. The KKE/D and GAR domains are shown in pink and green, respectively. B Diagram of states for the KKE/D domains of S. cerevisiae (Sc) Nop56, Nop58, Cbf5 and their H. sapiens (Hs) or S. pombe (Sp) homologs. The position of the GAR domains of Nop1 and Gar1 is also indicated. The red and blue areas correspond to strong polyelectrolyte features with FCR > 0.35 and net charge per residue >0.3 exhibiting coil-like conformations. C Classification of S. cerevisiae IDRs longer than 30 amino acids (n = 110) according to their Frequency of Charged Residues (FCR) and Net Charge as defined in Holehouse et al.⁶⁵. The size of each circle is proportional to protein abundance (Ho et al.⁶⁶). Blue and red circles correspond to GAR domain- and KKE/D domain-containing proteins, respectively. D Box plot showing the abundance of all nuclear proteins (n = 1076) containing IDRs longer than 30 amino acids. Specific outliers containing KKE/D and GAR domains are indicated. E KKE/D domain amino acid composition. The numbers correspond to the amino acid positions in the full-length sequence. *: C-terminus of the proteins. F Prediction of disorder tendency with PONDR⁶⁹. G Net charge per residue distribution obtained using CIDER (http://pappulab.wustl.edu/CIDER/analysis/) in the KKE/D domain of S. cerevisiae Cbf5. The region highlighted by the dotted rectangle corresponds to the large block of lysine doublets. H Amino acid sequence of the peptide corresponding to the block of lysine doublets of Cbf5 highlighted in (E), which was coupled to Alexa488 ([KKE/D]x9-Alexa488). I Bright-field transmission (trans) and fluorescence (Alexa488) images of coacervate droplets formed in vitro by the [KKE/D]x9-Alexa488 peptide in the absence (-) or in the presence of poly-U RNAs and in the absence or presence of 300 mM NaCl. Scale bar = 15 μm. J As in (I) but coacervates were formed by mixing the [KKE/D]x9-Alexa488 peptide with total RNA from S. cerevisiae in the absence or presence of 300 mM NaCl. Scale bar = 15 μm. Zooms within the indicated dotted squares are shown. Source data are provided as a Source data file.