Isolation of a cDNA clone encoding a biologically active thyroid hormone receptor.

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Abstract
We have isolated a c-erbA cDNA clone from a GH3 cell library. The clone, denoted erb62, is 4.5 kilobases long and encodes a 461-amino acid .beta.-type c-erbA protein. This c-erbA protein binds 3,5,3''-triiodothyronine (T3) and T3 analogs with affinities similar to those of the authentic T3 receptor. By RNA gel blot analysis, erb62 hybridizes to a 6-kilobase RNA found in organs that express T3 receptors .sbd.e.g., heart, kidney, and brain. A COS-cell transient cotransfection system was used to show that erb62 encodes a biologically active T3 receptor. An oligonucleotide, corresponding to a portion of the rat growth hormone gene 5''-flanking region that contains a T3 response element, was inserted on the 5'' side of the herpes simplex virus thymidine kinase promoter in a chloramphenicol acetyltransferase-expressing plasmid. Reporter gene expression directed by this hybrid promoter was T3 inducible only if this plasmid was cotransfected with an erb62-expressing plasmid.