This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Recher, L. Articles by Parry, N. T. Search for Related Content PubMed PubMed Citation Articles by Recher, L. Articles by Parry, N. T.

A Reevaluation of Nuclear and Nucleolar Changes Induced in Vitro by Actinomycin D¹

Southern California Cancer Center, Research Division, California Hospital Medical Center, Los Angeles, California 90015

Fine structural studies that included the use of various enzyme digestion procedures and autoradiography were carried out on ME-180 tissue culture cells treated with actinomycin D. Particular emphasis was placed on the evolution of the nucleolar changes that resulted from treatment with the antibiotic. Degradation of the nucleoloemal structure was the main effect of the drug. The fibrillar portion was involved first, indicating that it may contain an actively transcribing chromatin and may possibly be the site of synthesis of the 45 S precursor rRNA. The granular portion became involved later and gave rise to two fractions that, for convenience, were designated P₁ and P₂ fractions. All evidence indicates that P₁ granules, which have been shown to reside on fibrils, are precursors to P₂ granules, which lack such fibrillar support. It is suspected that P₁ granules contain 32 S RNA and P₂ granules contain 28 S RNA. Apart from granules, the P₂ fraction was shown to contain microspherules that were found to be composed primarily of basic proteins. These microspherules appear to be identical with those observed in cells treated with adenosine. Fibrillar centers were found to persist longest under the action of actinomycin D. Their close association with chromatin suggests a chromosomal origin. Since chromatin is the target structure of actinomycin D, it is postulated that all nucleolar alterations are due to chromatin changes induced by the antibiotic. It was shown that actinomycin D has a condensating effect on chromatin. Therefore, if a dispersed form of chromatin forms the skeleton of the nucleolonema, it would condense and thus cause the disintegration of the nucleolonema.

¹ This research was supported in part by the Albert Soiland Cancer Foundation.

Received 7/31/70. Accepted 9/29/70.

This article has been cited by other articles:

				Y. Shav-Tal, J. Blechman, X. Darzacq, C. Montagna, B. T. Dye, J. G. Patton, R. H. Singer, and D. Zipori Dynamic Sorting of Nuclear Components into Distinct Nucleolar Caps during Transcriptional Inhibition Mol. Biol. Cell, May 1, 2005; 16(5): 2395 - 2413. [Abstract] [Full Text] [PDF]

				R. Y.L. Tsai and R. D.G. McKay A multistep, GTP-driven mechanism controlling the dynamic cycling of nucleostemin J. Cell Biol., January 17, 2005; 168(2): 179 - 184. [Abstract] [Full Text] [PDF]