Identification in the rat prolactin gene of sequences homologous to the distal promoter of the human prolactin gene.

The goal of the present study was to test the hypothesis that a second, more distal, promoter exists upstream from the rat prolactin (PRL) gene (rPrl) that is homologous to that identified upstream from the human prolactin gene (hPrl). The nucleotide sequence of the rat genome extending from 7.4 to 2.5 kb upstream from the proximal rPrl promoter was determined, revealing significant sequence homology to the hPrl distal promoter and its 5'-flanking domain. Using reverse transcription-polymerase chain reaction, novel rPrl transcripts that originate upstream from the proximal rPrl promoter were detected in rat uterus, spleen, pons medulla, anterior pituitary and the GH4C1 pituitary tumor cell line. Further characterization of these novel 5'-extended rPrl transcripts from GH4C1 cells indicated that they were full length, polyadenylated and properly spliced. However, data from primer extension (5'-RACE) experiments strongly suggested that the 5'-extended rPrl transcripts originate, not at the distal promoter-like motif, but at scattered sites located 60-153 bp upstream from the proximal promoter. Therefore, it appears improbable that the rat sequences homologous to the hPrl distal promoter comprise a functional promoter.