A POINT MUTATION IN THE HUMAN ESTROGEN-RECEPTOR GENE IS ASSOCIATED WITH THE EXPRESSION OF AN ABNORMAL ESTROGEN-RECEPTOR MESSENGER-RNA CONTAINING A 69-NOVEL-NUCLEOTIDE-INSERTION

A novel ER-like mRNA containing a 69 nucleotide insertion precisely be tween exon 5 and 6 sequences was previously identified in human breast cancer biopsy samples. Data are presented which suggest that the 69 n ucleotide sequence is normally present in intron 5 of the human estrog en receptor gene. The region corresponding to and surrounding this 69 nucleotide sequence was cloned and the nucleotide sequence determined. Cloning and sequencing of the corresponding region in genomic DNA iso lated from a breast tumor expressing the 69 nucleotide inserted ER mRN A, revealed an A-->G point mutation immediately 3' to the 69 nucleotid e sequence. This point mutation resulted in the generation of a consen sus splice donor site. A consensus splice acceptor site sequence is no rmally present immediately 5' to the 69 nucleotide sequence. These dat a are consistent with the 69 nucleotide sequence being recognized as a n exon by the splicing machinery, and resulting in processing of a mat ure ER mRNA containing the 69 nucleotide insert.