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The karyotypes of females and males ofSphaerocarpos donnellii differ in that there is a large essentially heterochromatic X chromosome in the female (approx. 25 volume-% of the autosomes) and a small Y chromosome in the male (0.1–3 volume-% of the autosomes). DNA from females and males differ in buoyant densities in cesium chloride equilibrium gradients (1.7025 and 1.7035g cm-3, respectively) and in melting points (87.5 and 88.5°C in SSC). The differences are statistically significant. Base analyses revealed 2.5 Mol-% of the rare base 5-methyl cytosine. Upon reassociationSphaerocarpos DNA behaves kinetically in a heterogeneous manner. About 22% of the DNA is repetitive with an average kinetic complexity of 1.6×108 daltons. The kinetic complexity of the slow reassociating DNA fraction, considered to be of the single copy type, is 3.2×1010 daltons. No difference in the renaturation behavior between DNA of males and females could be detected with the techniques used. Our data thus indicate that X chromosomal DNA cannot contain large amounts of highly repeated nucleotide sequences and that it is slightly enriched in AT content compared to the autosomes.

1 DNA of DNase-treated mitochondria of Acanthamoeba castellanii bands at a buoyant density of 1.690 g/cm3. Up to 80% of the molecules were circular, with a circumference of 12.7 μm. Two circular conformations, the closed twisted and the open form, were separated in preparative CsCl–ethidium bromide gradients. 2 When mtDNA was renatured at a temperature Tm– 23°C, deviations from second-order kinetics were observed. At Tm– 10°C, however, it renatured as a single kinetic class without indications of sequence repetition. The coincidence of the kinetic complexity (2.57 × 107) and the circle contour length within the limits of error of the methods suggests that each circular molecule represents a chondriome. 3 The main DNA component, which is of nuclear origin and has a peak density of 1.716 g/cm3 in CsCl, displays heterophasic renaturation kinetics. Its slow-reassociating fraction shows a kinetic complexity corresponding to a molecular weight of 2.1 × 1010. Approximately 22% of the main component appears to be repetitive at a renaturation temperature of Tm– 23°C.

1. Chloroplast DNA of Antirrhinum majus, Oenothera hookeri, Beta vulgaris and Spinacia oleracea band at the same buoyant density of 1.697 g-cm-3 in neutral CsCl equilibrium gradients. The corresponding nuclear DNAs band at 1.691, 1.703, 1.695 and 1.695 g-cm-3, respectively. The purity of chloroplast and nuclear DNA can be assessed objectively only in the cases of Antirrhinum and Oenothera. 2. Electron microscopic analysis of chloroplast DNA, purified in CsCl or CsCl/ethidium bromide gradients, revealed up to 80% circular molecules. Of these about 15% were of supertwisted conformation. Best yields of circular molecules were recovered when populations of unbroken chloroplasts were subjected to DNAase and phosphodiesterase treatment, and when the DNA was purified from viscous lysates by centrifugation into a CsCl cushion. Treatment of plastids with DNAase alone did not guarantee complete degradation of nuclear DNA. 3. The average contour length of the open circular chloroplast DNA molecules was basically similar for all four plants. They were 45.9 plus or minus 2.1 mum for Antirrhinum, 45.7 plus or minus 1.9 mum for Spinacia, 44.9 plus or minus 1.7 mum for Beta and 45.2 mum for Oenothera. This is comparable to the size derived for the coding capacity of chloroplast DNA from reassociation experiments. As much as 15% of the total population of circles in chloroplast DNA of Spinacia were circular dimers.