{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"83997f0621e6ce02f7c86206a33c6c7db6dd00ffcda4c8c823b9053be9b67162","created":"2026-10-03T07:17:57Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"f09c11e05239f68e4bb87314f82efe16a389303e57b87ab7aead9b0798d0f28e","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"bio.cellular-sensing.extrinsic-noise-floor","kind":"phenomenon","literature_status":"open","n":"1","parents":[],"plain":"Genetically identical cells contain different amounts of each protein. For highly expressed proteins this variation stops shrinking at a floor that random chemistry at a single gene does not explain.","posed_since":"2010","precise":"In E. coli, the squared coefficient of variation of protein copy number, $\\mathrm{CV}^{2}$, falls as $1/\\langle n\\rangle$ at low mean copy number $\\langle n\\rangle$ but saturates at a floor of approximately 0.1 for highly expressed genes (Taniguchi and co-workers, 2010). Identify the cell-to-cell variables responsible (cell size, growth rate, cell-cycle phase, ribosome and polymerase content, partitioning at division) and predict the floor value quantitatively.","problem_ref":null,"references":"","settled_by":"Single-cell measurements that track the candidate global variables alongside protein levels and account for the floor value within experimental error.","status_note":"","title":"Origin of the extrinsic noise floor in gene 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