Identification of Polysomes Synthesizing Thyroglobulin

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Abstract
In preliminary experiments, we have shown that membrane‐bound thyroid ribosomes specifically synthesize thyroglobulin. This article presents more precise characterization of the thyroglobulin‐synthesizing polysomes. A population of heavy membrane‐bound polysomes has been isolated from horse thyroid in the detergent‐treated pellet of centrifugation at 27000 ×g. Immunoprecipitation experiments performed with labelled nascent peptides have revealed that this class of polysomes is specifically engaged inthyroglobulin synthesis. The pattern of [3H]uridine incorporation into these polysomes suggest that the thyroglobulin template has a very slow turnover. This is further supported by the unique resistance of these polysomes during long‐time incubations of thyroid slices with actinomycin D.