Fig. 1. OA1 is targeted to lysosomes in HeLa cells and to lysosomes and melanosomes in MNT1 cells. (A) Immunofluorescence analysis of HeLa cells transiently transfected with an expression vector for wild-type mycHis-tagged OA1. Exogenous OA1 was immunodecorated with anti-His₆ antibodies and lysosomes were labeled using the fluid-phase marker Lucifer Yellow by chasing for 1 hour prior to fixation (L.Y.). In the merge, areas of colocalization can be observed as yellow/orange. Bar, 10 µm. (B) Quantitative immunofluorescence analysis of the colocalization between endogenous OA1 and markers of various intracellular compartments in MNT1 cells. Cells were double labeled with anti-OA1 antibodies and with antibodies to LAMP1, Pmel17, TRP1, EEA1, or with Lucifer Yellow at 1 hour chase. Results are expressed as the percentage of double-positive vesicles out of all OA1-positive compartments per cell and represent the mean ± s.d. of the data pooled from one or two independent experiments. The number of vesicles and cells counted is indicated.