Fig. 8. FRET analysis of the interaction between Bax and Bak. (A,B) A sample record of CFP-Bax distribution (shown in red) and YFP-Bak distribution (shown in green) in an apoptotic HeLa cell. (C) Merged image of A and B. Arrows labelled 1, 2 and 3 indicate three different types of aggregates that were formed by (1) Bax alone, (2) Bak alone and (3) Bax and Bak. Scale bar: 10 µm. (D) The three types of aggregates marked by arrows 1, 2 and 3 in panel C were magnified and are shown in the upper panels. Their corresponding images obtained by FRET measurements are shown in the lower panels. Line-scan measurements were conducted. (E-G) Results of line-scan measurements conducted on the FRET images shown in the lower panels of Fig. 8D. (H) A sample record of FRET measurement using the photobleaching method. YFP-Bak was photobleached in the region marked by a box. Line-scan measurements of CFP intensity were conducted along the lines drawn across the aggregates outside (arrow a) and inside (arrow b) the photobleached region. (I,J) Results of line scan measurements conducted on the CFP-Bax aggregate outside (I) (marked by arrow a in panel H) or inside (J) (marked by arrow b in panel H) the photobleaching region before and after photobleaching.