Probable mitochondrial adenylate carrier that catalyzes the transport of ATP, ADP and AMP, but not ADP-glucose. Recombinant BT1 shows a unidirectional mode of transport in intact E.coli cells. May function as a plastidial nucleotide uniport carrier required to export newly synthesized adenylates into the cytosol. May be involved in abiotic stress response. Inhibited by pyridoxal 5-phosphate but not mersalyl. Dually targeted to mitochondria and plastids. The N-terminal extension acts as plastidic transit peptide. Dual localization of BT1 does not seem to be due to alternative transcription start sites, translation initiation sites or alternative exon splicing (PubMed:21330298). Expressed in root tips, the central cylinder of young roots, and maturating and germinating pollen. Impaired growth, flower and silique development, and production of shrunk and sterile seeds. The growth retardation observed in plants silencing BT1 is circumvented by adenosine feeding. Belongs to the mitochondrial carrier (TC 2.A.29) family.