Expression of a mutant vasopressin gene: differential polyadenylation and read-through of the mRNA 3' end in a frame-shift mutant.

Sequence analysis of cDNA clones derived from hypothalamic mRNA of diabetes insipidus (Brattleboro) rats shows that the vasopressin gene transcript also includes the single base deletion demonstrated in the gene. This causes a frame-shift in the C terminus of the vasopressin precursor with a reading frame open through the 3' end of the mRNA including the poly(A) sequence. Antibodies raised against a synthetic tetradecapeptide (CP-14) corresponding to the frame-shifted C terminus identified a product of mol. wt approximately 26 000 in a reticulocyte lysate system programmed with Brattleboro hypothalamic mRNA. Immunohistochemical analysis indicated that a similar precursor is also present in vivo in neurones of the Brattleboro hypothalamus. Electrophoretic analysis of vasopressin mRNA from wild-type and mutant rat tissues revealed that (i) the hypothalamic mRNA from Brattleboro rats contains a longer stretch of poly(A) sequence than the wild-type strains; (ii) vasopressin mRNA is also present in the adrenal, ovary, testis and cerebellum, at very low levels; however, (iii) the extra-hypothalamic mRNA is considerably shorter than that in the hypothalamus because of a curtailed poly(A) sequence. Thus similar vasopressin gene transcripts are subject to a tissue-specific differential polyadenylation.