The 3a protein domains and mutants. The 3a protein has three transmembrane regions (grey boxes) between amino-acid 34–56, 77–99, 103–125, and YXXΦ and EXD motifs in the 150 amino-acids long cytoplasmic domain. The Cyto3a mutant lacks the three trans membrane regions. The amino acid changes in the ∆YXXΦ and ∆EXD mutants are indicated. An N terminal c-Myc epitope tag (red box) is attached to all the constructs.