Chemical and conformational changes in chromosome regions being actively transcribed

Ubiquitin genes and ubiquitin protein location in polytene chromosomes of Drosophila

Ubiquitin genes are found in Drosophila either as a repeat block or as gene fusions with ribosomal proteins. Here is described the location of a new repeat block in the X chromosome that is present in the strain Canton S but absent in Vallecas. There are also two ubiquitin-ribosomal protein fusion genes located at regions 97A of chromosome 3R and 31E of 2L. Using an anti-ubiquitin antibody in Drosophila polytene chromosomes it is shown that ubiquitin is mainly associated with the compact and stabilized structure that forms the bands rather than with the more decondensed and destabilized protein-DNA structure that forms interbands and puffs.

Z-DNA in transcriptionally active chromosomes

Due to the striking correlation between the distribution of transcriptionally active subdivisions of the polytene chromosomes and Z-DNA, we have addressed the question of whether the Z-DNA configuration exists in native, transcriptionally active chromosomes of Drosophila hydei prepared without interference by procedures known to induce the B to Z conformation. Our experiments indicate that Z-DNA forms are present in a specific set of sites on the native chromosomes. They occur on interbands and other subdivisions of dispersed DNA, but there is no correlation between the amount of Z-DNA detected and DNA compaction. The results suggest, moreover, that Z-DNA forms are restricted to specific genes, because various subdivisions induced to transcription in puffs show different patterns of Z-DNA. We show, in addition, that removal of chromosomal proteins by proteinase K has a strong influence on the level of anti-Z-DNA reactivity.

In situ immunofluorescent visualization of chromosomal transcripts in polytene chromosomes

The induction and distribution of chromosomal transcripts in the polytene chromosomes of D. melanogaster and D. hydei has been investigated by indirect immunofluorescence using an antiserum directed against DNA/RNA hybrids. The fluorescence was intense and occurred in most of the chromosomal subdivisions when the chromosomes were exposed to denaturing conditions and then allowed to reanneal. The extent of hybrid formation depended both on the extent of DNA denaturation and on the maintenance of RNA integrity. Fluorescence was absent from chromosomes treated with pancreatic RNase before denaturation. The velocity of the chromosomal DNA/RNA hybridization reaction and the effects of the initiation inhibitor of RNA synthesis, DRB, suggest that in order to hybridize the RNA has to be located in its transcriptional compartment. Even though overall patterns of fluorescence seem to be similar during a developmental stage, variations were observed, particularly some correlated with puff induction after ecdysone stimulation.

Isolation of a structural gene mapping to subregions 63F of Drosophila melanogaster and 90B of D. hydei polytene chromosomes

We have isolated by molecular cloning techniques a structural gene that maps to subregion 63F of Drosophila melanogaster chromosome 3L. This locus being one of the early chromosomal targets for ecdysone stimulation, may be induced to puff by the hormone. The gene is on a plasmid vector and it has been designated as pDm 63F. This recombinant molecule also maps to the early ecdysone inducible subregion 90B of Drosophila hydei chromosome 4. The cytological inspection of large number of chromosomal sets after in situ hybridization of the cloned DNA, locates the cloned sequence between bands 63F 2-4 according to Bridges map. Similarly, in Drosophila hydei the cloned DNA maps between subdivisions 90B 2-4 according to Berendes' map. In situ hybridization of the pDm 63F cloned DNA, directed to the nascent RNA rather than to the DNA, shows two to three times more silver grains over the corresponding regions when puffed than in the resting stage. There are however quantitative differences attending to the transcriptional activity of homologous loci in both species. By RNA excess hybridization we have found that the cellular concentration of the 63F cloned mRNA is bout 2 times higher in hormone stimulated total larval tissues than in non-stimulated ones.

Non-histone chromatin proteins during various stages of activity of immunocompetent cells

Qualitative and quantitative changes of non-histone chromatin proteins of spleen cells during the primary immune response to sheep red blood cells and aggregated human gamma-globulin were described. Synthesis of non-histone chromatin proteins was measured by labelling with 3H-tryptophan during culture of spleen cells in vitro. Chromatin was isolated and labelled proteins were analysed by polyacrylamide gel electrophoresis. During the immune response to both antigens in chromatin of spleen cells three new fractions of non-histone chromatin proteins were synthesized: fractions F1 - M = 12 000 and H - M = 3 000, specific for sheep red blood cells and fractions I1 - M less than 3 000 and B - M = 120 000, specific for human gamma-globulin. The third antigen-non-specific fraction was synthesized at the time when the primary immune reaction was finishing. These new fractions were synthesized only in one of the analysed subpopulations of spleen cells. In thymocytes (non-fully-differentiated lymphoid cells) all these fractions were absent. Changes of non-histone chromatin proteins in thymocytes during the immune response were similar to those found during stimulation to proliferation by phytohemagglutinin in vitro.