FIGURE 4:

Serine substitution in the P-motif promotes constitutive ER–Golgi transport. (a) Subcellular localization of the precursor form of wt and DSG, 3S, and 3S+DSG mutants. (i–iv) Variants with intact cleavage sites for S1P and S2P. (v–viii) Variants with mutated cleavage sites. The S1P/S2P background status is indicated as wt or (S1P^-/S2P⁻) at the left-hand side. Cells were transiently transfected and after 48 h fixed in 4% paraformaldehyde and processed as described in Materials and Methods for immunofluorescence using anti-SV5 epitope (red channel) and anti-TGN46 (green channel) primary antibodies. (b) Higher-magnification image for the typical Golgi pattern obtained for 3S+DSG mutant in the context of the S1P⁻/S2P⁻ background. The 3S+DSG mutant in this context showed almost quantitative constitutive localization in the Golgi and the absence of any nuclear product.