Quick Definition
What is Tet-Free FBS?: Tet-Free FBS (tetracycline-free FBS) is fetal bovine serum confirmed to contain no detectable tetracycline or doxycycline. It is required for inducible gene expression systems (Tet-On, Tet-Off, TRE-based systems) where trace tetracyclines in standard FBS cause constitutive or leaky transgene expression independent of the inducer.
Why standard FBS interferes with Tet systems
Tetracyclines in standard FBS originate from cattle feed additives and veterinary antibiotics. Trace amounts (1–100 ng/mL) remain after processing. In a Tet-On system where doxycycline at 10–1,000 ng/mL drives transgene expression, even 10 ng/mL background from FBS creates partial activation — making the uninduced control unreliable with high background/induction ratio.
Diagnosing Tet system leakiness from FBS
If your Tet-On cell line shows expression in the uninduced state, test by replacing your current FBS with Tet-Free FBS. If background expression drops, FBS tetracycline contamination was the cause — one of the most common findings in inducible expression system troubleshooting.
Key Facts
- Standard FBS may contain trace tetracyclines from cattle feed — typically 1–100 ng/mL
- Tet-On systems are induced by doxycycline at 10–1,000 ng/mL — trace FBS tetracyclines cause significant background activation
- Tet-Off systems are suppressed by tetracycline — trace FBS tetracyclines partially suppress expression even without added inducer
- Tet-Free FBS tested by HPLC or bioassay — confirmed below detection limit for tetracycline and doxycycline
- Used at same concentration as standard FBS (10%) — direct replacement, no adaptation required for most cell lines
- Also required for: CRISPR screening with doxycycline-inducible guides, shRNA knockdown systems, synthetic biology tet-responsive circuits
Further Reading
SeamlessBio GmbH · Passau, Germany · info@seamlessbio.de
English 
Deutsch