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S P Modak

Publications and source records attributed to S P Modak.

At least 37 records · Page 2Linked to original sources
PubMed1984

Chromatin prepared using micrococcal nuclease retains the enzyme activity which can be removed with cation-exchange resin AG 50 WX2.

Micrococcal nuclease used to digest nuclei remains bound to the chromatin in an inactive form. The enzyme activity can be restored in situ by addition of divalent cations such as Ca++ or Mg++ resulting in continued digestion of high molecular weight chromatin into smaller fragments as demonstrated by two dimensional gel electrophoresis of samples as chromatin and DNA in the first and second dimensions, respectively. The bound enzyme can be selectively removed from the chromatin by treatment with cation exchange resin AG 50 WX2 at low salt concentration without altering the electrophoretic mobility of the chromatin.

Animals↗
PubMed1984

Immunochemical characterization and quantitative distribution of crystallins in the epithelium and differentiating fibre cell populations of chick embryonic lens.

Lenses from 19-day chick embryos are fractionated by a double punch method to obtain the epithelium-annular pad complex (EP), outer fibres (OF), middle fibres (MF) and central fibres (CF). Water-soluble crystallins are characterized by SDS PAGE, isoelectric focusing (IEF) and two-dimensional IEF-SDS PAGE. Crystallins are also characterized by immunoelectrophoresis (IE), rocket IE, IEF-immunoblotting, and quantified by two-dimensional antigen-antibody crossed electrophoresis using antibodies to total 19-day embryonic as well as adult crystallins. In the adult lens, alpha-, beta- and delta-crystallins are 19%, 67% and 14%, respectively, while these are present at concentrations of 9%, 27% and 64%, respectively, in 19-day embryonic lens. In absolute amounts, delta-crystallin increases only by 1.23-fold between 19-day embryonic age and 6 months post-hatching, while total lens protein increases 12.5-fold. The predominance of delta-crystallin in central fibres, located along the optical axis, suggests that this protein is of embryonic origin. delta-Crystallin from fibres is electrofocused as 12 distinct molecular classes (pI 5.2-5.42) which react against anti-delta-crystallin on an immunoblot. Of these, the three most anodal species are not detected in EP. Fibres contain 50 000, 48 000 and 45 000 dalton delta-crystallin subunits while only 50 000 and 48 000 dalton subunits are present in EP.

Animals↗
PubMed1980

Selective removal of histone H1 from nucleosomes at low ionic strength.

The method for removal of histone H 1 from chromatin by treatment with ion-exchange resin AG 50 WX 2 in the presence of 100 mM NaCl and 50 mM phosphate buffer (Thoma and Koller, 1977, Cell, 12, 101-107) results in production not only of H1-depleted chromatin but also free DNA. We have not modified this procedure so that the nucleosome is treated with the cation exchange resin in two steps, first in 50 mM sodium phosphate buffer and then in 50 mM sodium phosphate and 50 mM NaCl whereby histone H 1 is selectively removed without a release of free DNA at low resin concentrations.

Cation Exchange Resins↗
PubMed1980

Analysis of DNA double- and single-strand breaks by two dimensional electrophoresis: action of micrococcal nuclease on chromatin and DNA, and degradation in vivo of lens fiber chromatin.

We describe a novel system for two dimensional electrophoresis at neutral and alkaline pH for determining the double-stranded and single-stranded lengths of DNA. With this system we analysed the mode of micrococcal nuclease digestion of DNA in cellular and SV40 viral chromatin and of supercoiled SV40 DNA. The enzyme reaction occurred in two steps : the enzyme first introduced single-strand breaks, then converted these to double-strand breaks by an adjacent cleavage on the opposite strand. Digestion of cellular chromatin DNA occurred by a similar mechanism. Chromatin fragments produced by limited micrococcal nuclease action contained many single-strand breaks, which may be important when this method is used to prepare chromatin fragments for biochemical and biophysical studies. Nucleosome monomer to tetramer produced at later stages of digestion contained few if any single-strand breaks.

Animals↗
PubMed1979

Longevity, stability and DNA repair.

The functional capacity of a cell, tissue, organ, or organism is dependent upon its ability to maintain the stability of its unit components. The higher the differentiated state of the system, the greater the amount of stability required to maintain that state as a function of time. Stability can be achieved via either redundancy or repair. Redundancy while easily achievable in biological systems is both costly and limited by thermodynamic considerations. Repair, in its general sense, has no such limitations. Repair at the cellular and macromolecular level is multiple in its forms and varies as a function of species, tissue, and stage of the cell cycle. The repair of DNA damage is a dynamic process with many components and subcomponents, each interacting with one another in order to achieve a balance between individual stability and evolutionary diversity. Thus, between internal and external factors which damage DNA and the subsequent expression of alterations in the functional stability of DNA lie the multi-functional pathways which attempt to maintain DNA fidelity. A strong correlation between ulta-violet light induced excision or pre-replication repair, as measured by autoradiogrphy and maximum species lifespan has been reported within different strains of the same species, between related species (e.g. Mus musculus and Peromyscus leucopus), between five orders of mammals, and most recently within members of the primate family. As has been demonstrated by the authors and others, differences in excision repair between species and tissues may relate to the turning off of portions of the repair processes during embryogenesis. Regardless of why such correlations exist or the nature of their mechanisms, it is naive to either assert or deny a causal role for DNA repair in longevity assurance systems. For example, while species-related differences in DNA repair may reflect the turning off of such repair processes during fetal development this does not mean that rates of accumulation of DNA damage are not altered by such changes. Indeed, such a phenomena might well explain the rapid evolution of lifespan within the primates without a concurrent input of new genes.

Aging↗
PubMed1979

Gel electrophoretic analysis of histones in lens epithelium, lens fiber, liver, brain, and erythrocytes of late chick embryos.

Histones from 19-day-old chick embryo lens epithelium, lens fibers, liver, brain, and erythrocytes were electrophoresed in polyacrylamide gels using buffers containing sodium dodecylsulfate, acetic acid urea, or mixtures of Triton X-100 acetic acid urea. In the last two buffer systems, histone bands were characterized by their apparent molecular weights determined by electrophoresis in the second dimension in sodium dodecylsulfate containing polyacrylamide gels. From the densitograms of the stained gels, the relative proportion of protein in different histone bands was estimated. With the exception of the erythrocyte-specific histone H5, all histones from different tissues examined at any of the gel systems migrated with the same mobilities. In lens epithelium and lens fibers, all histones were present in identical proportions. As compared to liver and brain, the total amount of histone Hl was significantly lower in lens cells and erythrocytes, possibly reflecting differences between the differentiated states. However, no tissue-specific differences were found in the relative distribution of histone Hl I and Hl II among lens epithelium, lens fiber, liver and, brain, but a threefold higher Hl I : Hl II ratio (0.5--0.7) was found in erythrocytes.

Animals↗
PubMed1978

Preparative density gradient centrifugation of RNA and DNA in cesium sulfate-urea mixture.

A new procedure is described for a large scale separation and purification of unfixed DNA and RNA from a mixture of partially extracted nucleic acids and lysates of subcellular fractions by centrifugation to equilibrium in cesium sulfate-urea mixture. Optimum conditions are described for the separation and quantative recovery of both RNA and DNA in a pure form. The procedure allows determination of peak buoyant densities of 4-5s RNA, 7-11s mRNA and total cytoplasmic RNA. The procedure also allows fractionation of small molecular weight classes of cytoplasmic RNAs from the 18s and 28s rRNAs.

Animals↗
PubMed1977

DNA degradation in terminally differentiating lens fiber cells from chick embryos.

During the terminal differentiation of lens fiber cells, nuclear DNA is known to accumulate free 3'-OH ends and is progressively lost from the nucleus. Toward the end of this process, nuclei undergo pycnosis and disappear. The size of the DNA in the epithelia and in early and late stages of fiber cell development was examined by electrophoresis on nondenaturing agarose/polyacrylamide gels. Low molecular weight DNA of discrete sizes appears only at the final stages of nuclear degeneration in central fiber cells and persists after the disappearance of the nuclei. These low molecular weight DNA fragments appear as multiples of a monomeric unit and are similar to the fragments produced by the digestion of epithelial cell nuclei by micrococcal nuclease. The data indicate that in lens fiber nuclei the double-strand breaks in vivo affect the chromatin during nuclear degeneration, and the data suggest that the DNA of these cells is organized into chromatin composed of discrete subunits.

Animals↗
PubMed1975

DNA synthesis in circulating erythroblasts of anemic duck. Isolation and properties of nuclear and cytoplasmic-nonmitochondrial DNA.

In the circulating blood of anemic ducks, 5% of all erythroid cells synthesize DNA. Immature erythroblasts, at all stages of differentiation, synthesize DNA although to a varying degree, while reticulocytes and erythrocytes do not. In the erythroid cell population labeled in vitro 2 h with 32Pi, half of the labeled DNA sediments as small-molecular-weight molecules, suggesting that these molecules fail to integrate into the high-molecular-weight components. Labeled DNA is found in the cytoplasmic postmitochondrial fractions and it is in a form of deoxyribonucleoproteins which cosediment with ribosomes as well as subribosomal particles in sucrose gradients. However, fixation with HCHO and centrifugation to equilibrium in CsCl gradient of these particles shows that the deoxyribonucleoprotein bands at the density different than the ribosomes and, thus, not physically linked to them. In EDTA-dissociated ribosomes, the deoxyribonucleoprotein particles cosediment with ribosomes as well as subribosomal particles in sucorse gradients. However, fixation with HCHO and centrifugation to equilibrium in CsCl gradient of these particles shows that the deoxyribonucleoprotein bands at the density different than the ribosomes and, thus, not physically linked to them. In EDTA-dissociated ribosomes, the deoxyribonucleoprotein particles cosdeiment with ribosomal subunits in such a way that the larger the particle, the larger the molecular weight of the DNA cosedimenting with it. The specific radioactivity of the cytoplasmic ribosome-derived and postribosomal-particle-derived DNAs and the small molecular-weight nuclear DNA is similar and 10-20-fold higher than that of the bulk nuclear DNA. The former three DNA species sediment between 4-14 S. It is concluded that the cytoplasmic nonmitochondrial DNA species are of the nuclear origin. Less than 0.5% of the total cellular nonmitochondrial DNA can be purified from the nucleus and the cytoplasm as fast-labeled small-molecular-weight components. All of the cellular nonmitochondrial DNA species band at the same mean buoyand density in Cs2SO4/urea gradients. All behave as native structures in hydroxyapatite and contain less than 5% of their length as single-stranded regions.

Anemia↗