biostudies-literatureUnknownHe SNIGMS NIH HHSBiomolecular condensates spatially organize cellular functions, but the regulation of their size, number, dissolution, and re-condensation is poorly understood. The pyrenoid, an algal biomolecular condensate that mediates one-third of global CO₂ fixation, typically exists as one large condensate per chloroplast, but during cell division it transiently dissolves and reconfigures into multiple smaller condensates. Here, we identify a kinase, KEY1, in the model alga <i>Chlamydomonas reinhardtii</i> that regulates pyrenoid condensate size and number dynamics throughout the cell cycle and is necessary for normal pyrenoid function and growth. Unlike wild type, <i>key1</i> mutant cells have multiple smaller condensates throughout the cell cycle that fail to dissolve during cell divisiobioRxiv : the preprint server for biology2025.10.09.681382https://www.ebi.ac.uk/biostudies/studies/S-EPMC12632510biostudies-literatureKinase KEY1 controls pyrenoid condensate size throughout the cell cycle by disrupting phase separation interactions.PMC12632510R01 GM140032Kayser-Browne AJonikas MCLemma LMHennacy JHRai AKWingreen NSBrangwynne CPHe GWang CBunday LMartinez-Calvo AWang LHe SWang QErgun SLfalseKinase KEY1 controls pyrenoid condensate size throughout the cell cycle by disrupting phase separation interactions.Biomolecular condensates spatially organize cellular functions, but the regulation of their size, number, dissolution, and re-condensation is poorly understood. The pyrenoid, an algal biomolecular condensate that mediates one-third of global CO₂ fixation, typically exists as one large condensate per chloroplast, but during cell division it transiently dissolves and reconfigures into multiple smaller condensates. Here, we identify a kinase, KEY1, in the model alga <i>Chlamydomonas reinhardtii</i> that regulates pyrenoid condensate size and number dynamics throughout the cell cycle and is necessary for normal pyrenoid function and growth. Unlike wild type, <i>key1</i> mutant cells have multiple smaller condensates throughout the cell cycle that fail to dissolve during cell divisio2025-01-01T00:00:00Z2025 Oct2026-06-09T03:19:01.274Z2026-06-09T03:08:08.603ZS-EPMC126325104127883610.1101/2025.10.09.681382