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. 1974 Mar;71(3):894–898. doi: 10.1073/pnas.71.3.894

Induction of Nucleolar and Mitochondrial DNA Replication in Tetrahymena pyriformis

Jan Engberg *, Jytte R Nilsson †, Ronald E Pearlman ‡, Vagn Leick *
PMCID: PMC388122  PMID: 4207073

Abstract

Selective induction of replication of nucleolar and mitochondrial DNA has been demonstrated in starved-refed cultures of Tetrahymena pyriformis by different techniques.

Labeling of starved cells with [3H]thymidine during a nutritional shift-up and analysis of the DNA in isopycnic CsCl gradients shows that the two initially labeled species of DNA are two species banding on the heavy and light side of the bulk macronuclear DNA. In isolated macronuclei the radioactivity is found only in the high density fraction, which has been shown to be of nucleolar origin. In sucrose gradients the newly replicated mitochondrial and nucleolar DNAs sediment considerably slower than the bulk DNA, as one discrete band corresponding to a molecular weight of about 3 to 4 × 107.

Electron microscope autoradiography of cells labeled with [3H]thymidine as above shows that the peripheral nucleoli of the macronucleus as well as the mitochondria are labeled before any radioactivity is found in the chromatin granules of the macronucleus.

The results clearly indicate that nucleolar and mitochondrial DNA replication are under a control independent of that for the replication of bulk DNA.

Keywords: nutritional shift-up, CsCl gradients, EM-autoradiography, sucrose gradients

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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