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Multiple forms of mammalian deoxyribonucleic acid polymerase. An attempt to relate their interactions with nuclei and free deoxyribonucleic acid in vitro with their possible functions in vivo.

ABSTRACT: THE DNA POLYMERASES OF THE FOLLOWING EUKARYOTIC TISSUES WERE STUDIED: regenerating rat liver, normal rat liver, rat thymus, normal mouse liver and Ehrlich ascites-tumour cells. In all cases two main polymerase forms are observed, one of mol.wt. 200000, preferring denatured DNA to native calf thymus DNA primer, designated type I, and the other, designated type II, of mol.wt. 100000, showing a variable and slight preference for native calf thymus DNA primer. Some catalytic properties of these polymerases are described. Nuclei have been isolated from some of these tissues by using two different buffer systems. The ionic composition of the isolation medium is found to affect greatly the amounts and types of polymerase that bind to the nuclei, and also affects the kinetic properties of the polymerases. The way the polymerases and nuclei change properties as the ionic composition of the buffers is changed suggests that ionic effects may be a significant factor in the control of DNA synthesis in vivo. These ionic effects also explain much of the previous confusion over the localization of specific DNA polymerases.

SUBMITTER: Wallace PG

PROVIDER: S-EPMC1178024 | biostudies-other | 1971 Nov

REPOSITORIES: biostudies-other

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Project description:1. The stimulations of DNA-dependent RNA polymerase in isolated rat-liver nuclei by thyroid hormone, human growth hormone and testosterone are compared. 2. Single or multiple administrations of growth-promoting doses of tri-iodo-l-thyronine, human growth hormone and testosterone stimulate the Mg(2+)-activated RNA-polymerase reaction in nuclei from thyroidectomized, hypophysectomized and castrated rats respectively. The magnitude of stimulation was proportional to the degree of enhancement of liver growth by each hormone. After a single injection, the latent period preceding the stimulation was 1, 2 and 10hr. for growth hormone, testosterone and tri-iodothyronine respectively. The time-course of stimulation of enzyme activity and the synthesis of rapidly labelled nuclear RNA in vivo were also different for each hormone. 3. Growth hormone administration failed to stimulate the Mn(2+)/ammonium sulphate-activated RNA-polymerase reaction. Thyroid hormone and testosterone, however, stimulated it but the effect was less pronounced and occurred several hours later than that observed for the Mg(2+)-activated RNA-polymerase reaction. 4. In combination experiments, hypophysectomized or the thyroidectomized rats were given growth hormone or tri-iodothyronine in a single or repeated doses at levels that produced the maximum stimulation of Mg(2+)-activated RNA-polymerase activity. Taking into account the different latent period for each hormone, a single administration of the second hormone caused an additional stimulation of the enzyme activity. Similar additive effects were observed in thyroidectomized-castrated rats after treatment with tri-iodothyronine and testosterone. The magnitude of the additional stimulation caused by the administration of the second hormone was compatible with the capacity of that hormone to promote liver growth in rats deprived of it. 5. It is concluded that, although these hormones have some similar effects, the regulation of nuclear RNA synthesis may be mediated via different routes for each hormone.

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Multiple forms of mammalian deoxyribonucleic acid polymerase. An attempt to relate their interactions with nuclei and free deoxyribonucleic acid in vitro with their possible functions in vivo.

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