Figure 4.

Sumoylation delays protein entry into the nucleus. (A) The structures of the different ATF7 constructs are schematized. (B) Time laps microscopy monitoring of cells expressing GFP fused constructs ATF7WT, ATF7K118R or SUMO-GA-ATF7. HeLa-SUMO cells were transfected with 0.25 µg of the different plasmids as indicated. Twenty-four hours later 10 nM Dexamethasone was added to the culture medium (t = 0). The level of fluorescence in the nucleus was monitored using time laps microscopy. Bar: 20 nm. Quantification of the mean time required to reach a nuclear signal of same intensity as the one measured in the cytoplasm perinuclear region (cytoplasm/nuclear equilibration). Constitutively sumoylated ATF requires twice as much time as the other constructs to equilibrate the nuclear signal to the level of the cytoplasm.