The genetic analysis of D. melanogaster heterochromatin

Classical, or constitutive (Brown, 1966), heterochromatin is a nearly ubiquitous aspect of higher eukaryotic chromosome structure and its genetic significance has been debated since its first description (Heitz, 1928, 1929). This review describes genetic studies on the heterochromatin of Drosophila and the perspectives they provide on the possible biological role(s) of constitutive heterochromatin. In addition to documenting the existence of gene loci within heterochromatin, these studies provide evidence for long-range interactions within the nucleus and involving heterochromatin. These interactions may reflect more general properties of chromatin related to the three-dimensional structure of the interphase nucleus and its effects on gene expression.

Rye chromosome translocations in hexaploid wheat: a re-evaluation of the loss of heterochromatin from rye chromosomes

Using in situ hybridization techniques, we have been able to identify the translocated chromosomes resulting from whole arm interchanges between homoeologous chromosomes of wheat and rye. This was possible because radioactive probes are available which recognize specific sites of highly repeated sequence DNA in either rye or wheat chromosomes. The translocated chromosomes analysed in detail were found in plants from a breeding programme designed to substitute chromosome 2R of rye into commercial wheat cultivars. The distribution of rye highly repeated DNA sequences showed modified chromosomes in which (a) most of the telomeric heterochromatin of the short arm and (b) all of the telomeric heterochromatin of the long arm, had disappeared. Subsequent analyses of these chromosomes assaying for wheat highly repeated DNA sequences showed that in type (a), the entire short arm of 2R had been replaced by the short arm of wheat chromosome 2B and in (b), the long arm of 2R had been replaced by the long arm of 2B. The use of these probes has also allowed us to show that rye heterochromatin has little effect on the pairing of the translocated wheat arm to its wheat homologue during meiosis. We have also characterized the chromosomes resulting from a 1B-1R translocation event.From these results, we suggest that the observed loss of telomeric heterochromatin from rye chromosomes in wheat is commonly due to wheat-rye chromosome translocations.

Buoyant density fractionation of Drosophila melanogaster chromatin

Buoyant density fractionation of Drosophila melanogaster chromatin utilizing low molecular weight molecules such as actinomycin-D to induce changes in buoyant density has been investigated. Fractions of chromatin containing identifiable repeated DNA sequences could be isolated using actinomycin-D as the selective agent. Protein displacement from the chromatin complex was found to be a prerequisite for the observed buoyant density changes.

Characterization of DNA-Bound Histone in the Cells of The Avian Erythropoietic Series

The distribution of DNA-bound histone from purified cell populations of the avian erythroid cell series was studied to examine the possible relationship between these molecules and the in vivo activity of cells. High-resolution polyacrylamide gel electrophoresis of histones indicated that the 3 main cell types, namely, erythrocytes (inactive in macromolecular synthesis), polychromatic erythrocytes (active in RNA and protein synthesis) and erythroblasts (dividing cells) all contained the same histone components. This result is contrary to previous reports that the f2c histone (characteristic of avian erythroid cells) was absent from erythroblasts; in addition it does not support the proposition that dividing cells contain a unique f1 histone component. Quantitation of histone analyses showed that erythroblasts contain relatively less f2c histone than the non-dividing cells of the series and that there was a slight redistribution of f1 histone components between polychromatic and mature erythrocytes.