Heterogeneity in the polyglutamine tract of the glucocorticoid receptor from different rat strains.

The glucocorticoid receptor (GR) is a well characterised sequence specific DNA binding protein. Functional mapping of rat GR has shown that it consists of a C-terminal ligand binding domain, a central DNA binding domain and an N-terminal transactivation domain (for a review, see 1). Comparison of the amino acid sequence of the N-terminal domains of the human, mouse and rat GR reveals a polyglutamine tract, whose function is unknown, which varies in length between these species (see Figure). The rat GR cDNA cloned from both a hepatoma cell line, J.2.17.2 (2) and from prostate (3) was shown to contain a stretch of 21 glutamines whereas the mouse and human receptors contain 9 and 2 glutamines respectively (4, 5). We have isolated a genomic clone from a X library of Sprague—Dawley rat genomic DNA (Clontech) which contains the first coding exon of GR. Sequence analysis of this clone showed that the polyglutamine tract was only 7 amino acids long.