Regulation of stress granule maturation and dynamics by poly(ADP-ribose) interaction with PARP13.

Non-covalent interactions of poly(ADP-ribose) (PAR) facilitate condensate formation, yet the impact of these interactions on condensate properties remains unclear. Here, we demonstrate that PAR-mediated interactions through PARP13, specifically the PARP13.2 isoform, are essential for modulating the dynamics of stress granules-a class of cytoplasmic condensates that form upon stress, including types frequently observed in cancers. Single amino acid mutations in PARP13, which reduce its PAR-binding activity, lead to the formation of smaller yet more numerous stress granules than observed in the wild-type. This fragmented stress granule phenotype is also apparent in PARP13 variants with cancer-associated single-nucleotide polymorphisms (SNPs) that disrupt PAR binding. Notably, this fragmented phenotype is conserved across a variety of stresses that trigger stress granule formation via diverse pathways. Furthermore, this PAR-binding mutant diminishes condensate dynamics and impedes fusion. Overall, our study uncovers the important role of PAR-protein interactions in stress granule dynamics and maturation, mediated through PARP13.