The anion transporter AE1 (band 3) mediates electroneutral exchange of Cl^– for HCO₃^– across red blood cell membranes. Human AE1 is a 911-amino acid protein thought to traverse the plasma membrane as many as 14 times (Tanner, 1997). Previous work (Groves et al. 1998) showed that when human AE1 is expressed as two separate non-complementary fragments representing the entire protein but lacking the putative transmembrane (TM) helices numbers 6 and 7, the assembly can mediate ³⁶Cl influx into Xenopus oocytes. We have now created a single construct (band3(1:5-8:14)) composed of the N-terminal fragment of AE1, consisting of TM helices 1-5, covalently linked to the C-terminal fragment consisting of TM helices 8-14. Using a combination of pH-sensitive microelectrodes and a two-electrode voltage clamp, we have demonstrated that, while still capable of low level Cl^–-HCO₃^– exchange, the protein also mediates the conductive passage of anions. Xenopus oocytes expressing the ‘linked’ AE1 construct (band 3(1:5-8:14)), had a markedly higher membrane conductance (4.50 μS) than control AE1-expressing oocytes (0.2 μS). Substituting Cl^– in the bathing medium for gluconate, reduced the oocyte membrane conductance and shifted the zero current potential as expected for an anion selective pathway. Its permeability sequence was NO₃^–>NO₂^–>I^–>Cl^–~Br^–>formate^–>HCO₃^–>gluconate^–. Analysis of oocyte membrane patches expressing band 3(1:5-8:14) revealed single-channel events with a unitary conductance of ~35 pS, and an open probability of 2-3%. Such events were never observed in control oocytes. Each channel-bearing patch had a multiple of two functional channels, as if each AE1 dimer contained two channel pores. As proposed by Jennings (1989) the structure of AE1 includes an aqueous channel that penetrates deep into the membrane allowing anions access to the translocation site at the permeability barrier. Our finding, that the removal of TM helices 6-7 from AE1 is sufficient to give it channel-like properties, reinforces the idea that ion transporters and ion channels are not distinct membrane mechanisms, but are part of a continuum of ion-carrying proteins. Thus the anion selectivity of the access channel of AE1 may contribute to the high degree of selectivity exhibited by the native transporter.