Nucleolar protein 7 (Nop7), also known as PES1 or Pescadillo, is a conserved factor essential for ribosome biogenesis, cell cycle progression, proliferation, and nucleolar organization in yeast and metazoans. Its dysregulation has been linked to multiple human diseases. Here, we characterize Nop7 in Trypanosoma brucei and Leishmania major, microorganisms that possess atypical ribosomes whose 28S-type ribosomal RNA is multifragmented. In silico analyses indicates that trypanosomatids Nop7 exhibits putative structural adaptations that may support specialized protein-protein interactions. A PTP-tagged version of Nop7 localize to the nucleolus throughout cell cycle in both species. To define the Nop7 interactome, we performed tandem affinity purifications coupled with mass spectrometry, revealing extensive association with numerous transient trans-acting factors, including Erb1 and Ytm1, which together with Nop7 form a heterotrimeric complex (PeBow in mammals) essential for 60S ribosome subunit maturation. Comparative proteomic allowed us to identify several nucleolar proteins that represent potential parasite-specific factors needed for ribosome production. RNAi-mediated depletion of Nop7 in T. brucei impaired growth, disrupted morphology, and altered DNA content, underscoring its critical role in cell cycle progression and survival. Collectively, our findings provide the first proteomic map of Nop7-associated factors in trypanosomatids, revealing new candidates for future functional and therapeutic studies.
Nepomuceno‐Mejía et al. (2026) studied this question.