Intrinsic disorder specifies discreet functions of nucleoplasmin-like histone chaperones

Abstract

Nucleoplasmin (NPM) histone chaperones regulate distinct processes in the nucleus and nucleolus. While intrinsically disordered regions (IDRs) are hallmarks of NPMs, it is not clear if all NPM functions require these unstructured features. We assessed the importance of IDRs in yeast NPM-like proteins and found that regulation of rDNA copy number, and genetic interactions with the nucleolar RNA surveillance machinery require the highly conserved FKBP prolyl isomerase domain, but not the NPM domain or IDRs. By contrast, transcriptional silencing in the nucleus requires IDRs. We demonstrate that multiple lysines in poly-acidic serine/lysine motifs of IDRs are required for both lysine polyphosphorylation and NPM-mediated transcriptional silencing. These results demonstrate that NPM-like proteins do not rely on IDRs for all chromatin-related functions.