Journal of Cell Science, Vol 5, 27-44, Copyright © 1969 by Company of Biologists

Submitted on December 3, 1969

The Distribution of DNA Within the Nucleoli of the Amphibian Oocyte as Demonstrated by Tritiated Actinomycin D Radioautography

¹ Department of Biology, Yale University, New Haven, Connecticut, U.S.A.; Isotope Department, The Weizmann Institute of Science, Rehovoth, Israel

The distribution of DNA within the nucleoli of the newt oocyte has been studied using tritiated actinomycin D (³H-AD) radioautography. In the course of the study further evidence was found for the specificity of this technique. In many of the cytological preparations the specificity of binding was enhanced by extraction with ethanol after exposure to ³H-AD. The actinomycin D-DNA complex is somewhat unstable in cytological preparations. Incubation in buffers causes some dissociation of the complex; divalent cations accentuate the effect. The technique of ³H-AD radioautography was again shown to be more sensitive than Feulgen staining by the detection of ³H-AD binding in the Feulgen-negative forms of the nucleoli of the amphibian oocyte. The binding of ³H-AD to all of the nucleolar forms confirms the presence of DNA in these organelles. Results from this study and from others using [³H]uridine in the same system provide evidence that the nucleolar DNA is a detached loop-chromomere complex.