{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\nSTN1 is a critical component of the CST complex (comprising CTC1, STN1 and TEN1) that safeguards telomere integrity by binding single‐stranded DNA in a sequence‐independent manner. In mammalian cells, STN1‐containing CST associates with telomeres throughout the cell cycle to limit telomerase action, thereby ensuring that telomere extension is tightly regulated. CST acts in a manner reminiscent of replication protein A (RPA) by facilitating both proper replication of the telomere duplex and the crucial fill‐in synthesis of the C‐strand following telomerase-mediated G-strand extension. Such dual functions are evident from studies showing that reduction or loss of STN1 leads to aberrant single-stranded G-telomeric overhang accumulation, replication delays, and defects in C-strand synthesis, which ultimately compromise telomere length maintenance."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "5"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nBeyond its role in normal telomere replication, STN1 is essential for resolving replication stress. Depletion of STN1 not only compromises telomere duplication but also impacts genome-wide replication restart. Such stress is manifested as delayed progression through telomeric regions, accumulation of fragile telomeres, and enhanced sensitivity to agents that stall replication forks. Additionally, STN1-containing CST helps counteract the presence of obstructive DNA secondary structures (such as G-quadruplexes) during lagging-strand synthesis and is involved in coordinating the recruitment of repair and fork restart factors, including RAD51. These activities prevent unscheduled nucleolytic degradation at stalled forks and promote the firing of dormant origins in response to replication stress."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "6", "end_ref": "10"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nAt the biochemical level, STN1 contributes to the stimulation and organization of DNA polymerase-α–primase activity. Its N-terminal OB fold domain is primarily responsible for interacting with POLA2, a key subunit of the primase complex, thereby promoting the conformational changes necessary for efficient RNA-DNA primer synthesis. This regulatory interplay is crucial not only for initiating lagging-strand synthesis at telomeres but also for overall genome replication, reinforcing the concept that CST functions as an RPA-like molecular coordinator."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "11"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nRegulation of STN1 expression and its clinical importance further underscore its pivotal roles in maintaining genome stability. In budding yeast, STN1 levels are tightly controlled by translational mechanisms involving upstream overlapping open reading frames, a regulatory feature conserved in mammals that helps to fine-tune CST function. In humans, mutations in STN1 have been linked to telomeropathies such as Coats plus syndrome, where defective STN1 function leads to telomere dysfunction, genomic instability, and associated clinical phenotypes."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "13"}]}, {"type": "t", "text": "\n"}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Yasuyuki Miyake, Mirai Nakamura, Akira Nabetani, et al. 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