BINDING OF 3,5,3'-TRIIODOTHYRONINE (T3) AND ITS ANALOGS TO THE INVITRO TRANSLATIONAL PRODUCTS OF C-ERBA PROTOONCOGENES - DIFFERENCES IN THE AFFINITY OF THE ALPHA-FORMS AND BETA-FORMS FOR THE ACETIC-ACID ANALOG AND FAILURE OF THE HUMAN TESTIS AND KIDNEY ALPHA-2 PRODUCTS TO BIND T3

We have compared the affinities for T3and the T3 analog binding characteristics of the in vitro translational products of seven c-erbA cDNAs (chicken c-erbA α; human placental c-erbA β; rat c-erbA β-1; rat c-erbA α-1; rat c-erbA α -2; human testis c-erbA or-2; and human kidney c-erbA α -2). Four of these (chicken c-erbA α, human placental c-erbA β, rat c-erbA β-1, rat c-erbA α -1) bound T3 with high affinity as previously described. When compared under identical conditions of synthesis and [125I]T3 binding, there was no significant difference between the affinity of the chicken c-erb A α -1 and the human c-erbA β but in a more limited series the affinity of rat c-erbA β-1 for T3 was 4.6-fold higher than that of the rat c-erbA α-1. In vitrotranslational products of the β-probes showed a characteristic 2.2-fold higher triiodothyroacetic acid/T3 ratio than did the products of the α -probes, regardless of the species of origin of the probe. As previously established, the rat c-erbA α -2 product did not bind T3. However, in contrast to two published reports, the human testis and kidney α -2 probe products also failed to bind T3. These findings indicate that highly conserved C-terminal 37-40 residues are important for high affinity T3 binding by proteins encoded by the c-erb A family of genes. © 1990 by The Endocrine Society.