Structure and comparison of the oxytocin and vasopressin genes from rat.

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Abstract
The gene encoding the precursor protein to the hormone oxytocin and its associated neurophysin was isolated from a rat genomic library, and its sequence was determined. The small gene (.apprxeq. 850 base pairs) predicts a mRNA of .apprxeq. 500 bases [without the poly(A) tail]. The exon-intron organization is similar to that of the vasopressin gene, with 2 splice sites in the protein-coding region. The 1st exon (A) comprises the 5'' noncoding promoter region, a putative signal peptide, the nonapeptide hormone oxytocin, and the NH2-terminal, variable region of neurophysin. The 2nd exon (B) encodes the central, conserved region of neurophysin, and the 3rd exon (C) encodes the remaining COOH terminus of neurophysin, with an additional arginine residue at its end, presumably cleaved off during post-translational processing. A stretch of 143 nucleotides within exon B, except for a single base change, is entirely homologous to the equivalent part of the rat vasopressin gene, offering support for a gene conversion event having recently affected the 2 genes.