Nuclear basket protein ZC3HC1 and its yeast homolog Pml39p feature an evolutionary conserved bimodular construction essential for initial binding to NPC-anchored homologs of scaffold protein TPR

Abstract

Proteins ZC3HC1 and TPR are construction elements of the nuclear pore complex (NPC)-attached nuclear basket (NB). NB-location of ZC3HC1 depends on TPR already occurring NPC-anchored, whereas additional TPR polypeptides are appended to the NB by ZC3HC1. The current study examined the molecular properties of ZC3HC1 that enable it to bind to the NB and TPR. We report the identification and definition of a nuclear basket-interaction domain (NuBaID) of HsZC3HC1 comprising two similarly built modules, both essential for the binding to the NB's NPC-anchored HsTPR. Furthermore, we describe such a bimodular construction as evolutionarily conserved and exemplify the kinship of HsZC3HC1 by the NB- and DdTPR-interacting homolog of Dictyostelium discoideum and by characterizing protein Pml39 as the ZC3HC1 homolog in Saccharomyces cerevisiae. Among several properties shared by the different species' homologs, we unveil the integrity of the bimodular NuBaID of ScPml39p as being essential for binding to the yeast's NBs and its TPR homologs ScMlp1p and ScMlp2p, and we further present Pml39p as enabling interlinkage of Mlp1p subpopulations. In addition to phyla-specific features, we delineate the three species' common NuBaID as the characterizing structural entity of a one-of-a-kind protein found not in all but likely most taxa of the eukaryotic realm.