Heterogeneity in the 5′ untranslated region of the rat glucocorticoid receptor mRNA

We have cloned several novel sequences upstream from the first coding exon of the rat glucocorticoid receptor (GR) mRNA using PCR. Analysis of these sequences in RNase protection assays showed that one of the cloned sequences represents the major GR 5′ non-coding exon which is expressed in all tissues studied, both at different stages of development and under different hormonal conditions. This major exon is homologous to the human GR 5′ untranslated region (UTR). Three other sequences were cloned, but could not be detected in the RNase protection assay, suggesting that they are only minor transcripts, at least under the varying conditions of GR expression studied. One of these sequences is identical to a previously described rat GR cDNA sequence, while another was shown to be contiguous with the rat genomic DNA sequence.