Characterization of rat calcitonin mRNA.

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Abstract
A chimeric plasmid containing c[complementary]DNA complementary to rat calcitonin mRNA was constructed. Partial sequence analysis shows that the insert contains a nucleotide sequence encoding the complete amino acid sequence of calcitonin. Two basic amino acids precede and 3 basic amino acids follow the hormone sequence; calcitonin is apparently generated by the proteolytic cleavage of a larger precursor in a manner analogous to that of other small polypeptide hormones. The COOH-terminal Pro, known to be amidated in the secreted hormone, is followed by a Gly in the precursor. The cloned calcitonin DNA was used to characterize the expression of calcitonin mRNA. Cytoplasmic mRNA from calcitonin-producing rat medullary thyroid carcinoma lines and from normal rat thyroid glands contain a single species, 1050 nucleotides long, which hybridizes to the cloned calcitonin cDNA. The concentration of calcitonin mRNA sequences is greater in those tumors that produce larger amounts of immunoreactive calcitonin. RNA from other endocrine tissues, including anterior and neurointermediate lobes of rat pituitary, contain no detectable calcitonin mRNA.