Bcl-2 and Bax interactions in mitochondria probed with green fluorescent protein and fluorescence resonance energy transfer.

It has been hypothesized that interaction of Bcl-2 and Bax may regulate apoptosis. The spatial and temporal interaction of Bcl-2 and Bax at the single cell level has not, however, been demonstrated. To achieve this goal, we have developed two-fusion FRET (fluorescence resonance energy transfer). Using green fluorescent protein (GFP)-Bax and blue fluorescent protein (BFP)-Bcl-2 fusion proteins coexpressed in the same cell, we demonstrate a direct interaction between Bcl-2 and Bax in individual mitochondria. Mitochondrially localized cytochrome c-GFP and BFP-Bcl-2 showed little or no FRET, while nuclear-localized GFP-human papillomavirus E6 and BFP-Bcl-2 did not interact when coexpressed in the same cell. These findings indicate that two-fusion FRET provides an opportunity to examine the interaction between two different proteins coexpressed in single intact mammalian cells.