Different behaviour of Xbb+ and Xbb chromosomes in D. melanogaster with only one nucleolus organizer.

Summary We have examined the rDNA content of male and female adult flies having only one nucleolus organizer (NO), using X chromosomes carrying wild or partially deleted bobbed loci (Xbb ⁺/O, Xbb ⁺/X_NO-and Xbb/O, Xbb/X_NO ^-).The results show that in Xbb ⁺/O and Xbb ⁺/X_NO ^-flies, where only somatic gene compensation is supposed to occur, the rDNA increase, although less pronounced than previously reported, is directly proportional to the number of rRNA genes initially present in the nucleolus organizer. In Xbb/O and in Xbb/X_NO ^-flies the rDNA increase is relatively much higher than that observed in flies carrying bb ⁺ instead of bb. It is suggested that this may be due to rDNA premagnification and somatic gene compensation occurring simultaneously in the former flies.On leave of absence from International Institute of Genetics and Biophysics, Naples, Italy     

Natural antibodies to IFN-gamma in man and their increase during viral infection.

Natural antibodies to IFN-gamma were found in healthy individuals ranging from newborn babies to adults and, at higher levels, in patients suffering from different viral infections. During a viral infection, the titer of anti-IFN-gamma antibodies was observed to be correlated with the stage of the disease. Antibodies specific to IFN-gamma were affinity purified both from sera taken from healthy individuals and sera from viral-infected patients, by using a rIFN-gamma-coupled CNBr-activated Sepharose 4B column. The antibodies were found to be of the IgG class, and maintained their ability to bind rIFN-gamma. They were then tested for neutralizing activity and none of the IgG preparations we analyzed impaired the antiviral activity of rIFN-gamma. This finding suggests that the antigenic determinants recognized by these antibodies on the IFN-gamma molecule are located outside the site, on the IFN-gamma molecule, responsible for its antiviral activity.     

Conformational studies on bombesin antagonists: CD and NMR characterization of [Thr6, Leu13 psi(CH2NH) Met14] bombesin (6-14).

The conformational flexibility of the [Thr6, Leu13 psi(CH2NH) Met14] bombesin (6-14) nonapeptide has been studied by CD and one- and two-dimensional (1D and 2D) nmr techniques. The CD and nmr parameters in different solvents and in a micellar environment (SDS) are compared with the data collected for the parent bombesin (BN) and [D-Phe12, Leu14]BN. A preliminary investigation on spantide is also reported. In particular, the results obtained from CD measurements indicate that there is a shift from random coil structures, in aqueous solutions, toward folded structures in apolar media (2,2,2-trifluoroethanol) and in a membrane-mimetic environment (40 mM SDS) for all three peptides, namely BN, [D-Phe12, Leu14]BN, and [Thr6, Leu13 psi(CH2NH) Met14]BN (6-14). Spantide, which also possesses some inhibitory activity against BN but very little sequence similarity, even in water, shows an ordered conformation. Nuclear magnetic resonance parameters such as backbone NH-alpha CH coupling constant values, amidic temperature coefficients, and the presence of only sequential nuclear Overhauser effects have not provided, so far, any clear evidence for a preferential ordered structure in the peptides studied, and this may be due to rapid exchange among different conformers in the nmr time scale.     

Chromatin fine structure of the histone gene complex of Drosophila melanogaster.

We have used salt extractions of nuclei and long agarose gels to dissect the chromatin fine structure of the histone gene repeat of Drosophila melanogaster. Extraction of nuclei with 0.35 M KCl removes many non-histone chromosomal proteins but does not significantly disturb the overall nucleosome arrangement of the repeat unit. After extraction of nuclei with 0.55 M KCl, which also removes histone Hl, the basic arrangement of nucleosome core particles in the repeat unit is not greatly disturbed and the exposed DNA segments near the 5' ends of the histone genes are also retained. Extraction of nuclei with 0.75 M or higher KCl concentrations causes extensive nucleosome sliding and rearrangement with accompanying changes in the nucleoprotein organization of the histone gene complex and loss of the 5' hypersensitive sites. Our results indicate that the histone gene repeat displays a highly organized chromatin structure in vivo.     

A simple procedure for parallel sequence analysis of both strands of 5'-labeled DNA

Ligation of a 5'-labeled DNA restriction fragment results in a circular DNA molecule carrying the two 32Ps at the reformed restriction site. Double digestions of the circular DNA with the original enzyme and a second restriction enzyme cleavage near the labeled site allows direct chemical sequencing of one 5'-labeled DNA strand. Similar double digestions, using an isoschizomer that cleaves differently at the 32P-labeled site, allows direct sequencing of the now 3'-labeled complementary DNA strand. It is possible to directly sequence both strands of cloned DNA inserts by using the above protocol and a multiple cloning site vector that provides the necessary restriction sites. The simultaneous and parallel visualization of both DNA strands eliminates sequence ambiguities. In addition, the labeled circular molecules are particularly useful for single-hit DNA cleavage studies and DNA footprint analysis. As an example, we show here an analysis of the micrococcal nuclease-induced breaks on the two strands of the somatic 5S RNA gene of Xenopus borealis, which suggests that the enzyme may recognize and cleave small AT-containing palindromes along the DNA helix.     

Analysis of the chromatin assembled in germinal vesicles of Xenopus oocytes

We have injected circular DNA, labeled with 32P at a single restriction site, into germinal vesicles of Xenopus laevis oocytes in order to study the nucleosome arrangement on the assembled minichromosomes. Two types of genes were used in these studies, the somatic 5 S RNA gene unit of Xenopus borealis and the histone gene unit of Drosophila melanogaster. We find that injections of labeled DNA alone, at 1 ng DNA per oocyte, results in irregularly spaced nucleosomes and partially supercoiled DNA molecules. However, perfectly spaced nucleosomes are assembled and fully supercoiled DNA is recovered if 5 to 20 nanograms of cold vector DNA is coinjected with the labeled DNA. At the optimum chromatin assembly conditions, the nucleosomes are perfectly spaced with a 180 base-pair periodicity, but they are randomly positioned on the DNA. The assembly of a periodic chromatin structure is accompanied by a dramatic enhancement in the expression of the injected 5 S RNA gene.     

ELECTRON MICROSCOPY OF MEMBRANOUS BODIES AND GENOPHORE IN CHLOROPLASTS OF BOTRYOCLADIA BOTRYOIDES (RHODYMENIALES, RHODOPHYTA)1

An ultrastructural study on the chloroplasts of the red alga Botryocladia botryoides( Wulfen) J. Feldmann has been carried out to investigate the morphology of globular membranaous bodies (MBs) located between thylakoids. These membranous bodies show an electron dense lumen, in which a pair of denser cores occasionally occurs. The lumen is electron transparent in the chloroplasts of vacuolized, non-dividing cells. The surface of MBs is in contact with the fibrils representing the plastidial genophore; the fibrils sometimes bridge the surface of MBs with the nearest thylakoid. In some planes of section a membranous stalk connecting a MB with thylakoids has been made evident .
Because the presence of similar bodies in chloroplasts and mitochondria of other red algae, as well as in mitochondria of yeast in which an intense synthesis of DNA occurs, the authors propose that MBs in red algae have a role in the replication of the genophore .