Investigation of the origin of variant, truncated estrogen receptor-like mRNAs identified in some human breast cancer biopsy samples.

Variant, smaller sized, estrogen receptor-like mRNAs have been previously cloned and sequenced from human breast cancer biopsy samples. In this study we have found that one variant estrogen receptor-like mRNA, clone 24, which is expressed in only one tumor, consists of sequences from the normal ER gene which is found on chromosome 6 and sequences unrelated to the ER which are found normally on chromosome 12. A more commonly occurring variant estrogen receptor-like mRNA, clone 4, contains sequences from the normal ER gene and LINE-1 sequences. Similar but not identical LINE-1 sequences have been found in some of the intervening sequences of the normal ER gene. The generation of these transcripts may involve either alternative splicing or trans-splicing mechanisms.