ELECTRON-MICROSCOPIC STUDIES OF CONDENSED MITOTIC CHROMOSOMES IN THE FISSION YEAST SCHIZOSACCHAROMYCES-POMBE

By blocking cells in mitosis with the anti-fungal drug thiabendazole, it has been possible to carry out ultrastructural studies on the condensed chromosomes of the fission yeast, Schizosaccharomyces pombe. It is estimated that the DNA in these chromosomes is compacted approximately 1000-fold, and that the nucleoprotein density is similar to that of higher eukaryotic metaphase chromosomes. A basic structural component of the condensed chromosomes appears to be a 50-60 nm fiber, which is often visible in a loop configuration on the periphery of the chromatids. This is reminiscent of the 50-60 nm fiber loops which are frequently seen in preparations of metaphase chromosomes, and suggests that mechanisms of nucleoprotein folding may be similar in both lower and higher eukaryotes.