Isolation and Characterization of a cDNA Encoding a Chicken β Thyroid Hormone Receptor

Abstract

We have isolated and characterized a cDNA encoding a chicken β homolog of c-erbA, or thyroid hormone receptor (TR). Chicken liver cDNA libraries were screened with a rat TRβ-1 cDNA probe, and several cDNA inserts were isolated and characterized. The sequence of one cDNA predicts a 369-amino-acid open reading frame (ORF), with a protein sequence that possesses 96% identity with that of rat TRβ-1, but only 88% identity with chicken TRα. These data indicate that the cDNA likely encodes a β form of TR that has the expected putative DNA and T₃ binding domains. The chicken TRβ (chTRβ) in vitro translated protein binds T₃ with high affinity, and binds both the thyroid hormone response element (TRE) from the rat growth hormone gene and the Xenopus vitellogenin A2 gene estrogen response element (ERE), similarly to that of the rat TRβ-1. Northern blot analysis revealed the expression of a 7.0-kb RNA in several tissues including cerebellum, pituitary, kidney, and liver. This chicken liver TRβ cDNA sequence varies in both the 5′ and 3′ untranslated regions from the chicken kidney TRβ cDNA sequence recently reported (Forrest et al., 1990). The 5′ untranslated cDNA sequence divergence occurs near a potential splice site junction of the human TRβ gene, suggesting that this chicken liver cDNA may represent an alternatively spliced RNA product of the chicken TRβ gene.