|Ultrastructural Organization of Yeast Chromatin.|
Rattner JB, Saunders C, Davie JR, Hamkalo BA
Journal of Cell Biology (1982)
Category: chromatin structure ¤ Added: May 06, 2004 ¤ Rating: ◊◊
The ultrastructural organization of yeast chromatin was examined in Miller spread preparations of samples prepared from spheroplasts or isolated nuclei of Saccharomyces cerevisiae . Micrographs from preparations dispersed in 1 mM Tris (pH 7 .2) illustrate that the basic chromatin fiber in yeast exists in two ultrastructurally distinct conformations. The majority (up to 95%) of the chromatin displays a beaded nucleosomal organization, although adjacent nucleosomes are separated by internucleosomal linkers of variable lengths. Ribonucleoprotein (RNP) fibrils are only occasionally associated with chromatin displaying the conformation . The remaining 5-10% of the chromatin appears to be devoid of discrete nucleosomes and has a smooth contour with a fiber diameter of 30- 40A. Transcriptional units, including putative ribosomal precursor RNAgenes, defined by the presence of nascent RNP fibrils are restricted to chromatin displaying this smooth morphology . Chromatin released from nuclei in the presence of 5 mM Mg` displays higher-order chromatin fibers, 200-300 A in diameter; these fibers appear to be arranged in a manner that reflects the two forms of the basic chromatin fiber.