HEp-2 cells co-expressing F and G proteins showing co-localisation of F and G proteins. Cells expressing either (A) the G protein or (B) the F protein were stained using anti-FLAG and anti-cmyc respectively and imaged using confocal microscopy at an optical plane corresponding to the cell periphery and cell top. (C) Cells co-expressing the F and G proteins were stained using anti-FLAG and anti-cmyc and imaged using confocal microscopy at an optical plane corresponding to the cell top and cell periphery. (D) Co-localisation was calculated using regions (white circles) within the co-transfected cells. WCC(1)-weighted co-localisation coefficient (green channel), WCC(2)-weighted co-localisation coefficient (red channel), Mand- Manders overlap coefficient, R Pearson’s correlation coefficients. (E) An example of the scatter-plot region from one of these circles is shown. The x-axis (1) denotes green pixel distribution, the y-axis (2) denotes red pixel distribution and region 3 denotes the yellow pixel combination (co-localising pixels).