This is a family of nucleoside transporters. In mammalian cells nucleoside transporters transport nucleoside across the plasma membrane and are essential for nucleotide synthesis via the salvage pathways for cells that lack their own de novo synthesis pathways [2]. Also in this family is mouse and human nucleolar protein HNP36 Swiss:Q14542 a protein of unknown function; although it has been hypothesised to be a plasma membrane nucleoside transporter [2].

1: Cloning of the human equilibrative, nitrobenzylmercaptopurine riboside (NBMPR)-insensitive nucleoside transporter ei by functional expression in a transport-deficient cell line. Crawford CR, Patel DH, Naeve C, Belt JA; J Biol Chem 1998;273:5288-5293. PMID:9478986

2: Molecular cloning and functional characterization of nitrobenzylthioinosine (NBMPR)-sensitive (es) and NBMPR-insensitive (ei) equilibrative nucleoside transporter proteins (rENT1 and rENT2) from rat tissues. Yao SY, Ng AM, Muzyka WR, Griffiths M, Cass CE, Baldwin SA, Young JD; J Biol Chem 1997;272:28423-28430. PMID:9353301