Identification of a Rat c-erbAα-Related Protein Which Binds Deoxyribonucleic Acid but does not Bind Thyroid Hormone

c-erbA cDNAs encoding thyroid hormone-binding receptor proteins have been previously isolated from several species and tissues. We have isolated a novel rat c-erbA cDNA, r-erbA alpha-2, identical to the rat brain c-erbA alpha cDNA (which we refer to as r-erbA alpha-1) except at the 3'-end of the cDNA, which encodes an altered carboxy-terminal region of the predicted amino acid sequence. The r-erbA alpha-2 cDNA is most closely related to the human testicular c-erbA alpha cDNA. The apparent molecular weight of the in vitro protein product of this cDNA is 55 K, close to that predicted from the nucleotide sequence. The r-erbA alpha-2 protein binds a DNA fragment containing a putative T3-responsive sequence from the rat GH gene. However, the r-erbA alpha-2 protein product does not bind T3. RNA isolated from rat GH3 cells and various rat tissues contains at least three mRNAs hybridizing to c-erbA alpha probes. A predominant 2.6 kilobase mRNA hybridizes specifically to r-erbA alpha-2, while a 5.0 kb mRNA hybridizes to r-erbA alpha-1-specific cDNA probes. The r-erbA alpha-1-related 5.0 kb mRNA is down-regulated by T3 treatment in GH3 cells as has previously been described for the 2.6 kb mRNA. The r-erbA alpha-2 mRNA is most abundant in brain, whereas the r-erbA alpha-1 mRNA is found in highest concentration in brown fat and skeletal muscle. r-erbA alpha-1 mRNA, unlike r-erbA alpha-2 mRNA, is undetectable in testis. Southern analyses suggest that the r-erbA alpha-1 and r-erbA alpha-2 mRNAs are derived from a single gene transcript.