Mediates both influx and efflux of nucleosides across the membrane (equilibrative transporter). Mediates transport of adenine, adenosine and uridine, as well as several nucleoside analog drugs, such as anticancer and antiviral agents, including cladribine, cordycepin, tubercidin and AZT. Does not transport hypoxanthine. Optimum pH is 5.5 for adenosine uptake. Observed in a punctate intracellular pattern showing partial colocalization with late endosomes/lysosomes. Not detected at the cell surface. Widely expressed in both adult and fetal tissues. Highest levels in placenta, uterus, ovary, spleen, lymph node and bone marrow. Lowest levels in brain and heart. The disease is caused by variants affecting the gene represented in this entry. Belongs to the SLC29A/ENT transporter (TC 2.A.57) family. Truncated N-terminus.