Germline-specific nascent polypeptide-associated complex (NAC) subunits are predicted by bioinformatics tools to...

Recent work has identified germ cell-specific variants of the ribosome-associated Nascent Polypeptide-Associated Complex (NAC) in Drosophila melanogaster - termed germline NAC (gNAC). Their function appears to be largely governed by intrinsically disordered regions (IDRs). Such regions are known to mediate the assembly of protein complexes and the formation of biomolecular condensates via phase separation, and can regulate proteostasis through post-translational modifications. The goal of our study was to define the specific molecular features of gNAC proteins that could promote their propensity for phase separation using a bioinformatics approach. Our analysis revealed several distinctive characteristics consistent with drivers of phase separation: an atypical, biased amino acid composition; the presence of low-complexity repeats capable of forming cross-β structures; extended disordered regions that may undergo structuring upon oligomerization; a near-maximal score for spontaneous phase separation as predicted by the FuzDrop program. Furthermore, we identified a significant codon usage bias for specific amino acid residues within the gNAC coding sequences, suggesting potential regulatory mechanisms at the translational level. Collectively, these features delineate gNAC proteins as a unique class of factors likely capable of driving phase separation. We propose that gNAC may organize specialized ribosome complexes in the germline through phase separation mechanisms, such as forming proteostasis condensates on ribosomes to ensure the faithful expression of germ cell-specific proteomes.