Expression of HA-epitope–tagged 4.1R¹³⁵ and 4.1R¹³⁵▵E16 isoforms in transfected COS-7 cells. COS-7 cells were transfected with HA-epitope–tagged 4.1R¹³⁵ or 4.1R¹³⁵▵E16 isoforms, fixed with 3% paraformaldehyde, permeabilized with 0.5% Triton X-100, and processed for immunofluorescence using a polyclonal anti–HA-epitope tag antibody as primary antibody and anti–rabbit IgG coupled to FITC as secondary antibody. Three fields of cells transfected with each 4.1R isoform are displayed. 4.1R¹³⁵localized to the cytoplasm and to a lesser extent to the nucleus with exclusion of the nucleoli (a through c). Because the intensity of nuclear and cytoplasmic staining is very similar in cells transfected with 4.1R¹³⁵, we highlighted the nucleus of the cell shown in (c) by showing DAPI staining superimposed with the FITC staining (see inset in lower left corner of [c]). In contrast, 4.1R¹³⁵▵E16 was exclusively expressed in the cytoplasm with no staining of the nucleus (d through f). Scale bar: 10 μm.