Prolactin (PRL) mRNA from human decidua differs from pituitary PRL mRNA but resembles the IM-9-P3 lymphoblast PRL transcript.

The expression of the human prolactin (hPRL) gene is normally restricted to the anterior pituitary and the decidualized endometrium of the uterus. The human B-lymphoblastoid cell line IM-9-P3 ectopically expresses a PRL mRNA which is about 150 nucleotides larger than its pituitary counterpart even though the mature protein products appear identical. In the present study we show that human decidual and IM-9-P3 PRL mRNAs are similar in size, both being elongated relative to the pituitary transcript. The size difference persisted after removal of the 3' end poly(A) tract, whereas the PRL precursors synthesized in a cell-free translation system using mRNAs from the three tissues showed identical apparent molecular weights upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The elongation could therefore not be attributed to differences in the protein coding region or in the degree of polyadenylation and is suggested to reside in the 5' untranslated region of the molecule.