Poly(ADP-ribose) polymerase auto-modification and interaction with DNA: electron microscopic visualization.

The interaction between purified calf thymus poly(ADP-ribose) polymerase and its activating co-purified DNA (sDNA) was investigated by electron microscopy. We have shown that the enzyme-DNA complex possesses a nucleosome-like structure. The enzyme-bound DNA (sDNA) was found to be enriched in single-stranded regions and branched structures, presumed to be replication forks. The auto-ribosylated polymerase as well as the branched poly(ADP-ribose) formed were visualized by dark field electron microscopy during the auto-ADP-ribosylation reaction and the possible mechanism of this phenomenon is discussed.     

Microinjection of human cell extracts corrects xeroderma pigmentosum defect

Cultured fibroblasts of patients with the DNA repair syndrome xeroderma pigmentosum (XP) were injected with crude cell extracts from various human cells. Injected fibroblasts were then assayed for unscheduled DNA synthesis (UDS) to see whether the injected extract could complement their deficiency in the removal of u.v.-induced thymidine dimers from their DNA. Microinjection of extracts from repair-proficient cells (such as HeLa, placenta) and from cells belonging to XP complementation group C resulted in a temporary correction of the DNA repair defect in XP-A cells but not in cells from complementation groups C, D or F. Extracts prepared from XP-A cells were unable to correct the XP-A repair defect. The UDS of phenotypically corrected XP-A cells is u.v.-specific and can reach the level of normal cells. The XP-A correcting factor was found to be sensitive to the action of proteinase K, suggesting that it is a protein. It is present in normal cells in high amounts, it is stable on storage and can still be detected in the injected cells 8 h after injection. The microinjection assay described in this paper provides a useful tool for the purification of the XP-A (and possibly other) factor(s) involved in DNA repair.     

Reinvestigation of the shape and state of hydration of the skeletal myosin subfragment 1 monomer in solution

Hydrodynamic calculations lead to the conclusion that chymotryptic (or ethylenediaminetetraacetic acid) myosin S1 in solution (hydrated), at 1-5 degrees C, can be modeled as a prolate ellipsoid, with an axial ratio lying between p = 1.0 and 2.5 (major axis between 100.5 A, for p = 1.0, and 162.5 A, for p = 2.5). The degree of hydration is considerable (1.24 g/g for p = 2.5 and 2.02 g/g for p = 1.0). The dehydrated myosin head is pear-shaped under the electron microscope, and its narrowest part is located near the junction with the tail [Elliott, A., & Offer, G. (1978) J. Mol. Biol. 123, 505-519]. Mendelson & Kretzschmar [Mendelson, R. A., & Kretzschmar, K.M. (1980) Biochemistry 19, 4103-4108] have shown that the pear-shaped molecule does not predict the experimental X-ray scattering curve. Nor is this model able to predict the hydrodynamic values. The three-dimensional model for S1 used by Mendelson and Kretzschmar gives a rather good fit to the experimental X-ray scattering curve, but it does not predict the hydrodynamic values. In order to try to reconcile the three models and to fit the X-ray scattering curve and the hydrodynamic data, we suggest that, in solution, the S1 monomer has the shape of a prolate ellipsoid and that an inclusion of bound water exists at one extremity of the protein. The rest of bound water surrounds the protein. As first approximation, the dry protein and the hole are assumed to have the same shape as the hydrated molecule (prolate ellipsoid; p).(ABSTRACT TRUNCATED AT 250 WORDS)     

Arrangement of subunit IV in beef heart cytochrome c oxidase probed by chemical labeling and protease digestion experiments

The arrangement of subunit IV in beef heart cytochrome c oxidase has been explored by chemical labeling and protease digestion studies. This subunit has been purified from four samples of cytochrome c oxidase that had been reacted with N-(4-azido-2-nitrophenyl)-2-aminoethyl[35S]-sulfonate (NAP-taurine), diazobenzene[35S]sulfonate, 1-myristoyl-2-[12-[(4-azido-2-nitrophenyl)amino]lauroyl]-sn-glycero-3- [14C]phosphocholine (I), and 1-palmitoyl-2-(2-azido-4-nitrobenzoyl)-sn-glycero-3-[3H]phosphocholine (II), respectively. The labeled polypeptide was then fragmented by cyanogen bromide, at arginyl side chains with trypsin (after maleylation), and the distribution of the labeling within the sequence was analyzed. The N-terminal part of subunit IV (residues 1-71) was shown to be heavily labeled by water-soluble, lipid-insoluble reagents but not by the phospholipid derivatives. These latter reagents labeled only in the region of residues 62-122, containing the long hydrophobic and putative membrane-spanning stretch. Trypsin cleavage of native cytochrome c oxidase complex at pH 8.2 was shown to clip the first seven amino acids from subunit IV. This cleavage was found to occur in submitochondrial particles but not in mitochondria or mitoplasts. These results are interpreted to show that subunit IV is oriented with its N terminus on the matrix side of the mitochondrial inner membrane and spans the membrane with the extended sequence of hydrophobic lipid residues 79-98 buried in the bilayer.     

Purification and properties of a plasminogen activator from cultured rat prostate adenocarcinoma cells

Zymographic analysis of the supernates from confluent cultures of a rat prostate adenocarcinoma cell line, PA-III, revealed the existence of two molecular forms of specific plasminogen activators, one of molecular weight of approximately 80 000 and another of approximate molecular weight of 45 000, in sodium dodecyl sulfate. The low molecular weight form has been purified 364-fold in 66% yield from the culture medium by a combination of gel filtration on Sephacryl S-200 and affinity chromatography on Sepharose 4B-benzamidine. The purified material possessed a specific activity of 192 000 urokinase CTA units mg-1. This enzyme displayed activity toward human Glu1-plasminogen, characterized by a Km of 1.7 +/- 0.2 microM and a Vmax of 0.53 +/- 0.1 pmol of plasmin min-1 unit-1. A synthetic chromogenic substrate, H-D-Ile-Pro-Arg-p-nitroanilide (S-2288), was found for the activator. The enzyme possessed a Km of 0.33 mM and a kcat of 55 s-1 for S-2288. The activator was found to be a serine protease, inhibited by diisopropyl fluorophosphate (iPr2PF). At a concentration of 1 mM iPr2PF, and 30 nM enzyme, the half-time of this inhibition was 3.8 min. The 45 000 molecular weight enzyme was found to be inhibited by rabbit antibodies to human urokinase, thus characterizing the activator as a member of the urokinase class. The 80 000 molecular weight enzyme was not neutralized by anti-human urokinase but was neutralized by rabbit anti-human melanoma activator, likely allowing it to be classified as the tissue activator type.     

Thymus cell differentiation and in vivo T-cell migration. I. Migration of lectin-selected thymocytes

The in vivo quantitative distribution and tissue positioning of mouse thymocytes selected in vitro by Lyt phenotype and lectin binding properties were examined. Lyt 1+2- thymocytes were selected for by cytotoxic elimination; peanut agglutinin (PNA) and soybean agglutinin (SBA) binding and nonbinding thymocyte fractions were separated by an agglutinin technique. Selected cell suspensions were labelled in vitro with 51chromium (51Cr) or [3H]adenosine. Labeled washed cells were injected intravenously into syngeneic recipients which were killed at 1, 24 or 48 hr. In recipients of 51Cr-labeled cells, tissues were collected for gamma counting, and the overall percentage recovery of injected radiolabel from the various tissues was assessed. Tissues collected from recipients of [3H]adenosine-labeled cells were fixed, sectioned, and processed for autoradiography; the positioning of labeled cells within the tissues was determined. Selected Lyt 1+2-, PNA-, and SBA- sets all showed significantly enhanced entry into lymph nodes and intestinal lymphoid tissues. Entry of SBA+ cells into these tissues was comparable to that of peripheral T cells. PNA- and SBA- selected sets, but not Lyt 1+2- selected cells, also showed increased localization to the spleen and lungs, and decreased localization to the liver. By autoradiography, PNA- cells entered lymphoid tissues much more than PNA+ cells, and at 1 hr fewer PNA+ cells in spleen were associated with lymphoid follicles. At 24 and 48 hr almost all labeled cells in lymphoid tissues were positioned in T-dependent areas. These results suggest that enrichment for thymocyte subpopulations described as "mature" also enriches for cells with the ability to enter lymphoid tissue. They also suggest that interactions at other tissue sites are important in the determination of in vivo migration, and that surface carbohydrate composition is an important factor in this determination.     

Induction of repairable DNA damage in Escherichia coli and interaction with DNA in vitro by the radical cation of chlorpromazine

Studies were performed to determine the DNA interactions of and the induction of cytotoxic effects by the radical cation (CPZ+.) formed enzymatically from chlorpromazine (CPZ): in the presence of native DNA the lifetime of CPZ+. is markedly increased. The decreased reactivity of CPZ+. in the presence of native DNA and the concomitant increased viscosity of CPZ+.-DNA complexes strongly support the assumption that CPZ+. does form intercalation complexes with DNA. The relative strong bacteriotoxicity of CPZ+. hindered the accurate determination of mutagenesis in various Salmonella indicator strains, but a test for repairable DNA damage in Escherichia coli using various repair-deficient strains indicated that the cytotoxic action of CPZ+. is in part due to DNA alterations which can be excised in wild-type DNA repair-proficient strains. After activation of CPZ with long wavelength UV light, genetic effects are observed in S. typhimurium strain TA98, as well as in the E. coli tester strains. The possible role of CPZ+. in the photosensitization of CPZ is discussed.     

The effects of different concentrations of glycerol and dimethylsulfoxide on the metabolic activities of kidney slices

Kidney slices either were exposed to the cryoprotectants for 1 hr at room temperature and subsequently washed and incubated in fresh KR buffer containing only the radioactive metabolic tracers, or were immediately incubated for 2 hr at 37 °C in KR buffer containing the cryoprotectant and the tracers. Exposure to glycerol by incubation of kidney slices in Krebs-Ringer bicarbonate buffer containing varying concentrations of glycerol from 0 to 70% ($\text{v}\text{v}$) resulted in a pronounced inhibitory effect on the protein synthesizing activity, while thymidine incorporation into DNA and the α-aminoisobutyric acid uptake through the cell membranes were less affected. Exposure of the tissue to buffer containing dimethylsulfoxide (Me₂SO) in concentrations of 10 to 20% ($\text{v}\text{v}$) resulted in a stimulatory effect on metabolism. At higher concentrations, Me₂SO was toxic resulting in damaging effects on protein and DNA synthesis as well as on membrane integrity. The stimulatory effects of exposure to low concentrations of Me₂SO on protein and DNA synthesis in kidney slices were concluded to be the result of an increased transport of precursors through the cell membranes.     

Correlation between endogenous nucleosomal hyper(ADP-ribosyl)ation of histone H1 and the induction of chromatin relaxation.

The effect of poly(ADP-ribose) synthesis on chromatin structure was investigated by velocity sedimentation and electron microscopy. We demonstrate that locally relaxed regions can be generated within polynucleosome chains by the activity of their intrinsic poly(ADP-ribose)polymerase. This relaxation phenomenon is also shown to be NAD dependent and to be correlated with the formation of hyper(ADP-ribosyl)ated forms of histone H1. Evidence is also presented which suggests that hyper(ADP-ribosyl)ated histone H1 is neither released from the relaxed chromatin, nor does it seem to participate in polynucleosomal aggregation.     

Effect of pH on binding of agonists and antagonists to rat heart muscarinic receptors.

Insulin, epidermal growth factor (EGF), platelet-derived growth factor, multiplication-stimulating activity and 10% foetal-calf serum each stimulated the phosphorylation of a cytosolic Mr-22000 acidic heat-stable protein in Swiss mouse 3T3-L1 adipocytes. Phosphorylation of this protein was not stimulated by isoprenaline or dibutyryl cyclic AMP. The effect of insulin was maximal (3-fold increase) by 10 min; half-maximal stimulation was observed at 70 pM-insulin. Both [32P]phosphoserine and [32P]phosphothreonine residues were present in the Mr-22000 protein after insulin- and growth-factor-stimulated phosphorylation, but no [32P]phosphotyrosine. The major site of insulin- and EGF-stimulated phosphorylation appeared to be a threonine residue, in contrast with previously studied insulin-stimulated phosphorylation of serine residues. Insulin treatment appeared to result in a shift of the protein toward the anode on isoelectric focusing. Insulin and EGF present simultaneously did not lead to phosphorylation beyond that seen with each hormone singly. We surmise that insulin, EGF and perhaps other growth factors may activate a common protein kinase or inhibit a common protein phosphatase in 3T3-L1 adipocytes which acts on the Mr-22000 protein.