Hydroxyapatite fractionation procedures in the study of the mammalian genome

Characteristic features of the sonicated DNA of Agama agama agama L. (Reptilia, Agamidae) on hydroxyapatite columns, using mouse DNA as a reference

Hydroxyapatite column chromatography has been used to study some properties of the extensively sheared DNA of the Rainbow lizard, Agama agama agama. Reassociation studies show that the genome has a Cot1/2 of 370. Approximately 15% of the genome is highly repetitive in nature. This repetitive fraction is resolved into thermally stable and less stable fractions. The stable fraction has a base composition of 47% GC, higher than the 40.2% GC for the native DNA. This stable fraction is believed to be of recent origin. Chromatography of the total DNA of the lizard with linear gradients of phosphate buffer containing 1 M urea resolves it into two components which were shown by thermal fractionation, also in the presence of 1 M urea, to vary in base composition. This behaviour may be characteristic of reptilian genomes and may be used as a basis for studying the structural organisation of the reptilian genome.

Specific features of the structural organization of the mitochondrial genome in rat liver

The nature of intramolecular heterogeneity of mtDNA in the liver of white rats has been studied. The peculiarities of the melting curve, and the possibility of DNA fractionation of nucleotide compounds with hydroxylapatite (HA) column chromatography has shown the presence of sequences differing in the mean nucleotide content. A section of about 350 pairs in size repeated four times was found in the reassociation of most thermolabile fraction with a mean composition of 28% GC. These sections are well seen on the denaturation map of the recorded molecules formed in the range of temperature transition 'helix-coil'. The distance between the centers of fusible sections (in percentage of total length) is 32.5, 32, 14.0 and 21.5.

5-Methylcytosine in Chlorelle pyrenoidosa DNAs

The presence of 5-methylcytosine in Chlorella pyrenoidosa (strain 211/8b) DNA's has been investigated by means of paper chromatography and thermal chromatography on hydroxyapatite. It has been shown that nuclear DNA contains 3.5 mol% 5-methylcytosine whereas no significant amount of this base can be detected in chloroplast DNA. The thermal chromatography of nuclear DNA labelled from [6-3H]- or [Me-14C] methionine lead us to conclude that the 5-methylcytosine content is directly proportional to the G + C content of the various DNA fractions. The existence of methylated sequences in DNA is postulated and the biological function of the 5-methylcytosine is discussed.

Characterization of yeast ribosomal DNA

High-molecular-weight yeast ribosomal DNA, purified by preparative Hg2+/Cs2SO4 gradient centrifugation, was characterized using RNA-DNA hybridization, CsC1 gradient analysis and denaturation-renaturation experiments. The following conclusions are drawn from the results of these studies. 1. 55--60% of the total yeast rDNA is made up of sequences coding for 42-S ribosomal precursor RNA. 2. The mean length of the 42-S precursor cistrons corresponds to a molecular weight of 6.2 X 10(6). 3. The overall G + C content fo yeast rDNA is 42%. On the hand, both the segments coding for the nonribosomal excess RNA of the 42-S precursor and those specifying 26-S and 17-S rRNA have a higher G + C content of 46.9--47.5%. 4. The 42-S precursor cistrons are closely bound up with sequences rather low in G + C content (34--35%), which account for 40--45% of the total yeast rDNA. In contrast to the multiple 42-S precurosr cistrons which show very little or no base sequence divergence these intervening (A + T)-rich sequences display a considerable heterogeneity in base sequence.

Self-renaturing fractions in the separated strands of mouse satellite deoxyribonucleic acid

Pyrimidine- and purine-rich strands of Mus musculus satellite DNA prepared by alkaline CsCl-gradient centrifugation can self-renature to a variable extent to give partial duplexes with high thermal stability. These duplexes were purified by treatment with nuclease S(1) followed by hydroxylapatite chromatography, and have been shown by pyrimidine-tract analysis to be very similar in sequence to total reassociated satellite DNA. It is believed that the self-renaturing fractions result from variable contamination of each strand with fragments of the other, rather than from molecular inversions. The predominantly single-stranded properties of these fractions may be partly due to the ability of mouse satellite DNA strands to reassociate in non-stoicheiometric proportions.

The coparison of closely related groups of rodents by DNA-DNA annealing

Within the genus Apodemus, DNA from A. sylvaticus and A. flavicollis could be distinguished on the basis of reciprocal DNA/DNA annealing in agar, even when unfractionated DNA was used. In preliminary experiments, DNA from geographical races of A. sylvaticus could not be distinguished, nor could DNA from two closely related species of Peromyscus.

Within the species Mus musvulus, the fast-renaturing fraction of L-cell DNA, separated on a hydroxyapatite column, was able to discriminate between L-cell (originating from the C3H inbred strain) and NZB (New Zealand Black) inbred strain DNA in agar.