RNA modulates the formation of amyloid fibrils of hnRNPA1A through interactions with biomolecular condensates. The study shows that in the absence of RNA, hnRNPA1A forms condensates that promote aggregation and fibril formation at the interface of the condensates. When RNA is present, it modulates the transition from soluble to amyloid states of hnRNPA1A depending on the RNA/protein ratio. At low RNA concentrations, RNA promotes both condensation and amyloid formation, while at higher concentrations, condensation is suppressed, but amyloid formation continues over longer incubation times. The presence of RNA can also accelerate amyloid formation, possibly through increased local concentration or structural changes in the protein. The study also shows that amyloid fibrils localize at the interface of condensates, and that RNA can influence the orientation of fibrils. The findings suggest that RNA can modulate the kinetics and molecular pathways of amyloid formation by affecting condensation and phase transitions. The results highlight the role of heterotypic interactions between nucleic acids and proteins in the formation of pathological amyloid fibrils. The study provides insights into the mechanisms underlying the formation of amyloid fibrils in membraneless organelles and their association with neurodegenerative diseases.RNA modulates the formation of amyloid fibrils of hnRNPA1A through interactions with biomolecular condensates. The study shows that in the absence of RNA, hnRNPA1A forms condensates that promote aggregation and fibril formation at the interface of the condensates. When RNA is present, it modulates the transition from soluble to amyloid states of hnRNPA1A depending on the RNA/protein ratio. At low RNA concentrations, RNA promotes both condensation and amyloid formation, while at higher concentrations, condensation is suppressed, but amyloid formation continues over longer incubation times. The presence of RNA can also accelerate amyloid formation, possibly through increased local concentration or structural changes in the protein. The study also shows that amyloid fibrils localize at the interface of condensates, and that RNA can influence the orientation of fibrils. The findings suggest that RNA can modulate the kinetics and molecular pathways of amyloid formation by affecting condensation and phase transitions. The results highlight the role of heterotypic interactions between nucleic acids and proteins in the formation of pathological amyloid fibrils. The study provides insights into the mechanisms underlying the formation of amyloid fibrils in membraneless organelles and their association with neurodegenerative diseases.