Figure 1.

Targeting of GFP-tyrosinase and GFP-lysozyme to peroxisomes in human cells. Fluorescence of human COS7 cells expressing (a) GFP-lysozyme or DsRed2-SKL; (b) GFP-tyrosinase and DsRed2-SKL; or (c) GFP-lysozyme and DsRed2-SKL. Cells were observed 36 h after transfection (magnification 60 ×). Separate small images of the GFP fluorescence (green) and DsRed2 fluorescence (red) are shown to the left of each main picture, in which the two fluorescent images are overlaid. Areas in which red and green fluorescence coincide show as yellow. (a) Control experiments reveal that expression of GFP-lysozyme is an adjunct to the cellular punctuate fluorescence pattern independently of the presence of DsRed2-SKL. The figures show a punctate fluorescence pattern for GFP fusions with (b) human tyrosinase and (c) chicken lysozyme. Both proteins co-localize with DsRed2-SKL in human peroxisomes as demonstrated by the fluorescence overlay. Owing to the evolutionary conservation of PEX5 within the metazoans [7,13,33], a chicken protein (lysozyme) can be assayed in a human cell line and the species barrier is not an issue in this study.