1976. Chromosome ultrastructure in the basidiomycete fungus Schizophyllum commune. -Hereditas 84: 49-60. Lund, Sweden. ISSN oO18-066l. Received June 30,19 i6Composition and ultrastructure of the chromosomes of the basidiomycete fungus Schizophyllum commune FR. were studied by histochemical staining, electron microscopy and DNA-fiber autoradiography. The histochemical reactions used for the detection of histones gave positive results in spore and dikaryotic hyphal nuclei indicating the presence of histones. Electron-microscopical localization of ammoniacal silver reaction for histones showed that silver grains, about 2M)--400 A in diameter, appeared only in the nuclei. This is the strongest evidence that the basic protein found by means of Fast Green and sulfaflavine is histone. In spread spore chromatin the diameter of chromatin fibers ranged from 30 A to 120 A. Fibers were found to be composed of spherical subunits, chromatinomeres (90-100 A in diameter). The linear array of silver grains in the chromatin stained with ammoniacal silver resembles chromatinomere organization. This supports earlier assumptions that chromatinomeres contain histones. Basidiospores were found to contain 0.02 pg of DNA per haploid nucleus, which divided by the chromosome number (n=4) gives an average value of 1.6 mm of DNA per average chromosome. DNA-fiber autoradiography of labelled spore chromosomal DNA revealed molecules up to 2.2 mm in length. This is taken as evidence of "chromosome-sized" DNA molecules and a uninemic structure of eukaryotic chromosomes.

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