Identification of two hERR2-related novel nuclear receptors utilizing bioinformatics and inverse PCR

Identification of novel nuclear receptors based on the highly conserved DNA-binding domain (DBD) has previously depended mainly on low stringency hybridization of cDNA libraries and degenerate PCR. Establishment of the expressed sequence tag (EST) database in recent years has provided an alternative approach for the discovery of novel members of gene families. The rate-limiting step is the conversion of ESTs to full-length cDNA. This article describes the identification of two novel nuclear receptors (hERR beta 2 and hERR gamma 2) related to human estrogen-receptor-related receptor 2 (hERR2) by mining the EST database and retrieving of full-length cDNA via inverse PCR on subdivided primary cDNA library pools. The deduced protein sequences of hERR beta 2 and hERR gamma 2 contain 500 and 458 amino acid (aa) residues respectively. Sequence analysis revealed that hERR beta 2 and hERR gamma 2 respectively share 95% and 77% overall aa sequence identity with hERR2. However, the extra C-terminal domain in hERR beta 2 and extra N-terminal domain in hERR gamma 2 are not present in the closely related hERR2 or mouse ERR2 (mERR2). Extensive sequence verification revealed that hERR2 previously reported as a human gene is actually a rat gene, whereas hERR beta 2 is the true human ortholog of hERR2 and mERR2. Tissue distribution studies showed that hERR gamma 2 was expressed in a broader panel of tissues at a higher level than hERR beta 2. hERR beta 2 was mapped to cytogenetic locus 14q24.3 similar to-14q31, a region containing multiple loci involved in genetic diseases, including Alzheimer and diabetes. hERR gamma 2 was mapped to 1q32. Given the high sequence homology between hERR beta 2 and mERR2, the two receptors may have similar biological function in vivo. (C) 1999 Elsevier Science B.V. All rights reserved.