Association of DNA synthesis with the nuclear membrane in sea urchin embryos

DNA-lipid interactions in vitro and in vivo

The data on lipid-nucleic interactions and their role in vitro and in vivo are presented. The results of study of DNA-lipid complexes in absence and in presence of divalent metal cations (triple complexes) are discussed. The triple complexes represent the generation of cellular structures such as pore complexes of eucaryotes and "Bayer's junctions" of procaryotes. The participation of triple complexes in the formation of structure of bacterial and eucaryotic nucleoid and nuclear matrix is analysed. A model of formation of triple complexes and cellular structures and their role in DNA-lipid interactions are discussed.

Evidence for incorporation of N-acetylglucosamine in endogenous nuclear acceptors during the nuclear matrix preparation

1. The presence of glycoproteins within the nucleus of cell is now well established and the question arises on the nature of the nuclear glycosylation and the site of their glycosylation. 2. In order to study endogenous nuclear proteins acceptors, we have isolated a subnuclear fraction: nuclear matrix characterized by DNA, RNA, phospholipids and proteins content. Nuclear matrix acceptors were obtained from nuclei incubated with UDP-N-acetyl [14C]glucosamine. 3. In this report we describe the presence of three major glycoproteins labeled with N-acetyl [14C]glucosamine in the nuclear matrix fraction. We obtained gP32, gP67 and gP70 with pI values around 6.2, 6.5 and 8.2.

Identification of nuclear envelope proteins and glycoproteins which co-isolate with the nuclear protein matrix

Nuclear envelopes and nuclear matrices were isolated from rat liver nuclei. Although differences in polypeptide composition of the structures are evident on SDS gel electrophoresis, they have an almost identical distribution of concanavalin A-binding glycoproteins. These matrix-associated concanavalin A-binding glycoproteins derive entirely from the nuclear envelope and are recovered almost quantitatively in the matrix. They constitute easily identifiable markers for nuclear envelope association with matrix or other nuclear subfractions. Surface labelling of nuclei with 125I using solid-phase lactoperoxidase further confirmed that a large number of envelope-associated nuclear surface proteins co-isolate with the matrix. Protein kinase activity, as well as endogenous substrates for the kinase(s) are shown to be the same in both envelopes and matrix. Envelope-derived proteins and glycoproteins may comprise a substantial proportion of total matrix protein.

Localization of DNA polymerase alpha on the nuclear membrane in sea urchin embryos

Subnuclear localization of DNA polymerase alpha was studied in sea urchin embryos. Blastula nuclei treated with EDTA and potassium phosphate released subnuclear components bearing most of the nuclear DNA polymerase alpha. These components were suggested to be a part of nuclear membrane based on their buoyant densities (1.177 and 1.136 g/cm3) in isopyknic centrifugation and the nuclear pore-like structure. Contamination with DNA and endoplasmic reticulum membrane to the subnuclear components was shown to be negligible. These results suggested that DNA polymerase alpha associates with nuclear membrane of sea urchin embryos. Nuclear membrane deprived of DNA polymerase alpha was able to associate with nuclear DNA polymerase alpha from blastulae and the cytoplasmic enzyme of unfertilized eggs efficiently, but not with the cytoplasmic enzyme of gastrulae. This result suggests that the nuclear membrane is originates from the endoplasmic reticulum with which DNA polymerase alpha associates in unfertilized eggs.

A potential DNA replication complex isolated from sea urchin embryos by renografin gradient centrifugation

A complex containing deoxyribonucleic acid, protein and lipid has been isolated from the nuclei of the sea urchin Stronglocentrotus pupuratus by gentle lysis of nuclei and centrifugation of the lysate in a renografin gradient. The complex is similar in several respects to DNA-membrane complexes isolated by the sarkosyl M-band technique [1]. These include the following: 1, most of the cellular DNA is present in the complex but the bulk of the DNA may be removed by sonication or nuclease treatment; 2, nascent DNA is preferentially found in the complex; and 3, destruction of membrane/protein components removes DNA found in the complex.

Association of DNA polymerase alpha and beta with rough endoplasmic reticulum in sea-urchin eggs and changes in subcellular distribution during early embryogenesis

The subcellular distribution of DNA polymerase alpha and beta was examined in unfertilized eggs and embryos of the sea-urchin, Hemicentrotus pulcherrimus. In unfertilized egg homogenates, prepared in sucrose solution containing 5 mM 2-mercaptoethanol and 5 mM MgCl2, DNA polymerases equilibrated in isospycnic centrifugation as a single peak at a buoyant density of 1.261 g/cm3 (band I). This indicates that DNA polymerases associate with a cytoplasmic organelle. Band I was converted to bands II (1.227 g/cm3), III (1.177 g/cm3) and IV (1.146 g/cm3) by EDTA treatment. The RNA content of bands I, II, III and IV was approximately 0.34, 0.25, 0.10 and 0.04 mg/mg protein respectively. In isokinetic and isopycnic centrifugations both DNA polymerase and RNA cosedimented and coequilibrated. These results suggest that bands I, II, III and IV contain various amounts of ribosomes on a common structure. Examination by electron microscopy indicated that bands I, II, III and IV contained mainly monolayered membrane vesicles with different amounts of bound ribosomes. The content of ribosomes varied in the order: band I > band II > band III > band IV. Each band contained DNA polymerase with sedimentation coefficients of 5.8-7.6 S (sensitive to N-ethylmaleimide and aphidicolin) and 3.2 S (insensitive to these drugs). We conclude that almost all of DNA polymerases alpha and beta are localized on the rough endoplasmic reticulum in unfertilized eggs. Mixing experiments suggest that the association is specific and is not an artifact of homogenization. During development of embryos DNA polymerases associated with the membrane decreased with concomitant increase in the nuclear fraction. This suggests that the enzymes migrate from the cytoplasm to the nucleus. It is discussed that the role of the endoplasmic reticulum as a storage site of DNA polymerases in unfertilized eggs and the mechanism of translocation of DNA polymerases from the cytoplasm to the nucleus during early embryogenesis.

Isolation and characterization of polyoma uncoating intermediates from the nuclei of infected mouse cells

A method was developed which enabled the efficient recovery of polyoma uncoating intermediates from the nuclei of infected cells at early times after infection (15 min to 12 h). Cells were infected with radiolabeled virus and lysed with the detergent Nonidet P-40. The nuclei were then collected and sonicated, and the products were analyzed on sucrose gradients. The uncoating intermediate sedimented at 190S and was a viral DNA-protein complex closely associated with a structure of host origin. The host material associated with the 190S uncoating intermediate was determined by polyacrylamide gel electrophoresis and visualized by electron microscopy. The amount of 190S uncoating intermediate found in the nucleus increased with time after infection. The viral DNA was predominantly for I. All of the viral proteins were present in the 190S uncoating intermediate in amounts similar to those found in viral DNA-protein complex cores.

Protection of liposomal lipids against radiation induced oxidative damage

Liposomes were prepared from phospholipids extracted from biological membranes. A comparison was made between the peroxidation rate in handshake liposomes and in sonicated liposomes. The smaller sonicated liposomes were more vulnerable to peroxidation, probably because of the smaller radius of curvature, which results in a less dense packing of lipid molecules in the bilayer and a facilitated action of water radicals produced by the X-irradiation. High oxygen enhancement ratios were obtained, especially at low dose rates, suggesting the operation of slowly progressing chain reactions initiated by ionizing radiation. Three compounds were tested for their ability to protect the liposomal membranes against lipid peroxidation. The naturally occurring compounds reduced glutathione (GSH) and vitamin E(alpha-T) and the powerful radiation protector cysteamine (MEA). All three molecules could protect the liposomes against peroxidation. The membrane-soluble compound vitamin E was by far the most powerful. About 50 per cent protection was achieved by using 5 X 10(-6) M alpha-T, 10(-4) M GSH and 5 X 10(-4) M MEA. The fatty acid composition of the lipids altered drastically as a result of the irradiation. Arachidonic acid and docosahexanoic acid were the most vulnerable of the fatty acids. Very efficient protection of these polyunsaturated fatty acids could be obtained with relatively low concentrations of vitamin E built into the membranes.