“…The first is the "gain-of-function" theory, which is supported by the finding that T-URF13, an inner mitochondrial membrane protein, may form a pore and interfere with membrane activity in the cytoplasm of maize (5,6). In addition, ORF138, which forms a complex of over 750 kDa, has been proposed to act as a pore in the inner mitochondrial membrane in a sterile line of rapeseed (7). The second theory, the "loss-of-function" theory, is supported by the characterization of ORF522, which shares a similar N-terminal amino acid sequence with ORFB but competes with ORFB in binding to the ATP synthase (complex V) subunit in sunflowers to reduce the stability and efficiency of this complex (8).…”