(A) The tension sensor module (TSMod) consists of two fluorophores separated by a flagelliform linker sequence (GPGGA)8. Localization and estimated FRET efficiency of TSMod in (B) live and (C) paraformaldehyde-fixed vinculin −/− MEF cells. (D) The actin-binding vinculin tension sensor mutant (VinTS-I997A) consists of TSMod inserted after aa 883 of vinculin and a point mutation at aa 997. Localization and estimated FRET efficiency of VinTS-I997A in (E) live, (F) paraformaldehyde-fixed, and (G) vinculin immunofluorescently-labeled vinculin −/− MEFs. (H) The vinculin tension sensor (VinTS) consists of TSMod inserted after aa 883. Localization and estimated FRET efficiency of VinTS in (I) live, (J) paraformaldehyde-fixed, and (K) vinculin immunofluorescently-labeled vinculin −/− MEFs. FRET distributions of all sample images are provided in Supp. Fig. 3. (L) Mean FRET efficiency of TSMod (live, n = 454, N = 11; fixed, n = 378, N = 11), VinTS-I997A (live, n = 161, N = 11; fixed, n = 50, N = 2; Vinculin IF, n = 272, N = 5), and VinTS (live, n = 173, N = 13; fixed, n = 164, N = 6; vinculin IF, n = 98, N = 3) under various conditions. Following a Levene’s test, differences between (a) TSMod and VinTS-I997A and (b) VinTS was determined by a Welch’s ANOVA and Games-Howell Test. Error bars represent one standard error.