Localization of DNA topoisomerase II in Chinese hamster fibroblasts by confocal and electron microscopy

The localization of the 170- and the 180-kDa isoforms of the enzyme DNA topoisomerase II in growing Chinese hamster fibroblasts has been studied by confocal immunofluorescence microscopy and immunogold electron microscopy after labeling with affinity-purified isoform-specific polyclonal antibodies. Immunofluorescence and immunogold studies, together with quantitative image analysis, show that the two isoforms are present in the nucleoplasm and in the nucleolus. In the nucleoplasm both isoforms are frequently localized at the periphery of heterochromatin regions. In the nucleolus the immunofluorescence and immunogold signals relative to surface area are higher than in the nucleoplasm; both isoforms are localized predominantly in the fibrillar zones. During mitosis both isoforms remain detectable in the cytoplasm. The differential expression of the two isoforms during the cell cycle, observed in other studies, suggests that they have different functions, and their presence in both the nucleoplasm and the nucleolus suggests that these functions are required in both of these nuclear compartments.

Precise localization of the alpha-globin gene cluster within one of the 20- to 300-kilobase DNA fragments released by cleavage of chicken chromosomal DNA at topoisomerase II sites in vivo: evidence that the fragments are DNA loops or domains

We have mapped the position of the alpha-globin gene cluster in the 20- to 300-kilobase fragments of chromosomal DNA isolated from growing chicken HD3 erythroblastoid cells exposed to 4'-demethylepipodophyllotoxinthenylidene beta-D-glucoside. This epipodophyllotoxin traps functioning topoisomerase II molecules, the denaturation of which cleaves DNA and reveals their reaction sites. The DNA fragments, prepared by centrifugation in sucrose gradients, bind selectively to glass-fiber filters and are protected from lambda 5'-exonuclease, properties compatible with the presence of a topoisomerase II subunit bound to their 5' ends. Restriction enzyme cleavage of the fragments and hybridization with cloned alpha-globin-region probes reveal additional distinctive bands not seen in control DNA, allowing the localization of fragment ends near this gene cluster. The terminal regions of fragments from sucrose gradients or from field-inversion electrophoresis gels were also used to probe cloned regions of the gene cluster. Both approaches show that this cluster of three genes, which is not expressed in these cells, is located at a specific position in a approximately 20-kilobase DNA fragment. The upstream end of this fragment lies in a region that contains a site of DNA attachment to the nuclear matrix mapped by both in vivo and in vitro methods, and its downstream end is flanked by approximately 80% A + T sequences characteristic of matrix-attachment regions. These observations suggest that the DNA fragments are formed because topoisomerase II molecules can specifically and readily integrate into DNA at matrix-attachment regions and that the fragments represent entire DNA loops or domains.

Inclusion bodies in recombinant E. coli producing human calcitonin tetramer, as visualized by immuno-gold electron microscopy

Inclusion bodies are described in recombinant E. coli cells harboring plasmid for the expression of a synthetic gene coding for human calcitonin tetramer. The inclusion bodies are visualized by electron microscopy and the protein is identified by immuno-gold technique, using antibodies against synthetic human calcitonin. The diameter of the inclusion bodies is 1 micron on the average.

Determination of total and divided clearance without blood sampling and not using a whole-body counter or gamma camera

A method is suggested for the determination of total and divided clearance on the basis of one renal function-excretion. The method, which can also be used for hydronephrotic cases, does not involve blood sampling or the use of a whole-body counter or gamma camera. The method was applied to 73 patients, 14 of whom presented with hydronephrosis. Of the 73 patients, 12 were comparatively examined, and the divided clearance was simultaneously determined in three different ways: graphically, by the areas enclosed between the blood-clearance heart curve and the beginning of the secretion phase of the nephrograms; by catheterizing and measuring the excreted urine from each kidney in a well-crystal detector; by the suggested method without taking blood samples. There was good agreement between the results obtained by the last two methods.

Effect of chromatin decondensation on the intranuclear matrix

We have studied the effect of chromatin condensation on the morphology of the residual structures isolated from rat liver nuclei. DNAse I digestion followed by high salt extraction of nuclei in the presence of Mg++ yields residual structures consisting of a dense peripheral layer surrounding an internal network, similar to those described by Berezney and Coffey [6]. These structures are stable at low ionic strength in the presence of EDTA. When nuclei swollen in EDTA are digested with DNAse II in the presence of EDTA, structures devoid of internal network are obtained even without subsequent treatment with high salt. When swollen nuclei are exposed to Mg++ a specific recondensation of chromatin takes place. The residual structures from recondensed nuclei are similar to those isolated from control nuclei in the presence of Mg++. The results suggest that the integrity and stability of the intranuclear matrix are acquired in the course of the isolation procedure and this is favoured by chromatin condensation.

Nucleosomes and nonribosomal RNA transcription in early mouse embryo. An electron microscopic study

Zygotes from hyperovulated albino-mice isolated during the first several cleavages were spread according to the method of Miller and Bakken [28] in the presence and in the absence of Joy or in the presence of Sarcosyl. Our results show that: 1. already before the first division of the mouse zygote all chromatin is organized in nucleosomes, 2. nonribosomal RNA transcription starts during the first divisions, 3. chromatin fibers associated with nonribosomal RNA transcription have a nucleosomal structure and 4. the use of detergent Joy may destroy the nucleosomes of some chromatin fibers.