Western blot evidence that Bug22p is the antigen of a commercial anti-GTL3 antibody. Lanes: A1, molecular mass markers for lane A2; A2, anti-GTL3 labeling of a 10,000 × g supernatant of whole homogenized paramecia showing a positive band between 20 and 25 kDa; B1 and C1, total extracts of E. coli expressing GFP in the pPXV plasmid normally used for expression in Paramecium but which allows low expression in the bacteria; B2 and C2, E. coli expressing the GFP-Bug22p fusion; C3, molecular mass markers for lanes B1 to C2. The B series lanes were revealed with the anti-GTL3 antibody and the C series with the anti-GFP antibody. The asterisk indicates the level of the fusion protein that is recognized by both GTL3 and GFP antibodies.