FUNCTIONAL-CHARACTERIZATION AND CHROMOSOMAL LOCALIZATION OF A CLONED TAURINE TRANSPORTER FROM HUMAN PLACENTA

A cDNA clone highly related to the rat brain taurine transporter has b een isolated from a human placental cDNA library. Transfection of this cDNA into HeLa cells results in a marked elevation of taurine transpo rt activity. The activity of the cDNA-induced transporter is dependent on the presence of Na+ as well as Cl-. The Na+/Cl-/taurine stoichiome try for the cloned transporter is 2:1:1. The transporter is specific f or taurine and other beta-amino acids, including beta-alanine, and exh ibits high affinity for taurine (Michaelis-Menten constant approximate to 6 mu M). The clone consists of a coding region 1863 bp long (inclu ding the termination codon), flanked by a 376 bp-long 5' non-coding re gion and a 625 bp-long 3' non-coding region. The nucleotide sequence o f the coding region predicts a 620-amino acid protein with a calculate d M(r) of 69853. Northern-blot analysis of poly(A)(+) RNA from several human tissues indicates a complex expression pattern differing across tissues. The principal transcript, 6.9 kb in size, is expressed abund antly in placenta and skeletal muscle, at intermediate levels in heart , brain, lung, kidney and pancreas and at low levels in liver. Culture d human cell lines derived from placenta (JAR and BeWo), intestine (HT -29), cervix (HeLa) and retinal pigment epithelium (HRPE), which are k nown to possess Na+- and Cl--coupled taurine transport activity, also contain the 6.9 kb transcript. Somatic cell hybrid and in situ hybridi zation studies indicate that the cloned taurine transporter is localiz ed to human chromosome 3 p24-->p26.