Fig. 3.

Role of ferritin in the day/night regulation of iron uptake in exponentially growing cells of O. tauri. (A) Regulation of iron uptake through a day/night cycle. WT and ΔFtn cells were grown under day/night conditions for 5 d in Mf medium containing 0.1 µM Fe(III) EDTA and then were shifted to iron-free Mf medium until the exponential growth phase. Every 3 h, 50 mL (about 20 × 10⁶ cells/mL) of each culture were harvested. The cells were washed with iron-free medium before 1 µM of ⁵⁵Fe(III) citrate was added. The uptake rate of ⁵⁵Fe (ρ_Fe) was determined for 15 min. Data shown are means ± SD from three experiments. (B) Kinetics of ferritin loading. WT and ΔFtn cells grown as described in A were incubated beginning at dawn or dusk with 1 µM ⁵⁵Fe(III) citrate. (Upper) Ferritin was detected by autoradiography of proteins (25 µg per lane) on blue native PAGE at 480 kDa. (Lower) Quantitation of ferritin band intensity was normalized to the mean signal.