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Title: Protein biosynthesis in the thyroid gland : a study of control mechanisms
Author: Begg, Dorothy Juliette
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1966
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Abstract:
Preliminary investigations were carried out to devise means of estimating the amounts of RNA and DNA in the thyroid gland. A study was then made of the nucleic acid, protein and phospholipid content of the thyroid glands of different mammalian species, and relationships to thyroid weight and total body weight established. It was found that, with increasing size of mammal, the concentration of protein in the thyroid gland increases, whereas there is a diminution in the concentration of RNA and, to a smaller extent, of DNA and phospholipid. These findings can be correlated with an increase in follicle size in larger mammals, which results in more colloid in proportion to the number of cells. Calculations made from the data show, that the amount of protein in the thyroid glands of various mammals is maintained at a constant proportion, of body weight. However the number of cells in the thyroid gland does not increase in parallel with the size of the species and the larger mammals also have less RNA per cell. These observations suggest that the turnover of protein in the thyroid glands of larger mammals may be less rapid than in smaller mammals. Isotopic studies were then carried out using tissue slices and purified nuclei prepared from sheep thyroid glands to study the effects of TSH on thyroid RNA and protein metabolism. When slices of sheep-thyroid tissue were incubated with TSH and (14 C) adenine, it was found that TSH caused an increase in labelling of nuclear RNA and subsequently of cytoplasmic RNA, and that this increase was detectable in all thyroid RNA fractions after 3 hr. incubation. The incorporation of (14C) adenine into the RNA of isolated sheep-thyroid nuclei in vitro was also found to be stimulated by the presence of TSH in the incubation medium. Rat-liver nuclei were not responsive to TSH under the same incubation conditions, and addition of protein (bovine serum albumin) to the incubation medium had no effect on adenine uptake into thyroid nuclear RNA. TSH also stimulated the uptake of (32P) UTP into RNA in the presence of the other unlabelled ribonucleoside triphosphates. The effect of TSH on adenine uptake into thyroid RNA could be inhibited by treatment of the slices or the isolated nuclei with puromycin or actinomycin D. These findings suggest that the earliest effects of TSH on thyroid RNA metabolism involve the synthesis of both nuclear RNA and protein. However, addition of TSH to an incubation medium containing isolated sheep-thyroid nuclei had no significant effect on (14 C) leucine uptake into nuclear protein under conditions where it stimulated (14 C) adenine uptake into nuclear RNA. This suggests that the protein apparently involved in stimulation of nuclear RNA synthesis by TSH must contribute to only a small proportion of the total nuclear protein. Purified sheep-thyroid nuclei were then fractionated either by the procedure of Weiss (1960) or by that of Ramuz, Doly, Mandel and Chambon (1965) and assays of DNA-dependent RNA polymerase activity carried out using the three nuclear enzyme fractions obtained. Some Properties of these polymerase enzyme fractions were then characterized and the effect of TSH on DNA-dependent RNA polymerase activity examined. Direct addition of TSH at the start of incubation to assay mixtures containing these enzyme fractions had no effect on DNA-dependent RNA polymerase activity. Treatment of isolated sheep-thyroid nuclei with TSH under conditions where it is known to stimulate the uptake of (14 C) adenine into nuclear RNA was found to increase the ability of the "Ramuz" aggregate enzyme preparation to incorporate labelled UMP from UTP but not labelled AMP from ATP into RNA. However, no effect of TSH was apparent when MG2+ replaced Mn2+ during Polymerase assay. Puromycin treatment of sheep-thyroid nuclei, which had been incubated in the presence or absence of TSH prior to enzyme preparation, was found to decrease the DNA-dependent RNA polymerase activities of the enzyme fractions prepared by the procedure of Ramuz et al. (1965).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.776610  DOI: Not available
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