ChAM, a novel motif that mediates PALB2 intrinsic chromatin binding and facilitates DNA repair

The partner and localizer of breast cancer 2 susceptibility protein (PALB2) is crucial for the repair of DNA damage by homologous recombination. Here, we report that chromatin-association motif (ChAM), an evolutionarily conserved motif in PALB2, is necessary and sufficient to mediate its chromatin association in both unperturbed and damaged cells. ChAM is distinct from the previously described PALB2 DNA-binding regions. Deletion of ChAM decreases PALB2 and Rad51 accumulation at DNA damage sites and confers cellular hypersensitivity to the genotoxic drug mitomycin C. These results suggest that PALB2 chromatin association via ChAM facilitates PALB2 function in the cellular resistance to DNA damage.     

A critical role of costimulation during intrathymic development of invariant NK T cells

CD1d-restricted Valpha14(+) invariant NK T (iNKT) cells are a specialized alphabeta T cell subset that regulates both innate and adaptive immunity. Although costimulatory molecules are required for the activation of conventional T cells and for the development of Foxp3(+) T cells, their role in iNKT cell regulation is unclear. Here we report that mice deficient in CD80/CD86 and/or B7h exhibit severe defects in thymic iNKT cell maturation, associated with largely reduced iNKT cell number in the thymus and the periphery. We show that costimulation is necessary for the optimal expansion of postselected NK1.1(-) immature iNKT cells in the thymus and for the proper expression of the maturation markers T-bet and CD122. Surprisingly, costimulatory molecules on both hemopoietic and nonhematopoietic cells are required for iNKT cell development. Our results thus demonstrate a previously unknown function of costimulation in the intrathymic development of iNKT cells, distinct from that of conventional T cells and regulatory T cells.     

Stimulation of ethylene production by hydroxamic acid, in particular, by benzohydroxamic acid

The effects on the ethylene production of known inhibitors ofa cyanide-insensitive, alternative respiration in plants wereinvestigated using cotyledonary segments of cocklebur (Xanthiumpennsylvanicum Wallr.) seeds. Benzohydroxamic acid (BHAM) at3 mM stimulated ethylene production 4- to 8-fold over the control,but respiration of the segments was hardly affected at thatconcentration. The stimulatory effects of 3-chlorobenzohydroxamicacid (CLAM) and salicylhydroxamic acid were far smaller thanthat of BHAM. BHAM at 3 mM also markedly stimulated the ethyleneformation in the epicotyl or hypocotyl sections of etiolatedpea (Pisum sativum L.) and mung bean (Vigna radiata [L.] Wilczek)seedlings. Moreover, 3 mM BHAM further promoted the increasedethylene formation which was caused by administration of 1-aminocyclopro-pane-1-carboxylicacid (ACC) to the cotyledonary segments. The promoting effectsby BHAM and CLAM were also found in the conversion of ACC intoethylene in pea stem homogenates. (Received July 26, 1980; )     

Inhibitory effect of intracerebroventricularly-administered [D-Arg(2), beta-Ala(4)]-dermorphin (1-4) on gastrointestinal transit

The inhibitory effect of intracerebroventricularly-administered [D-Arg(2), beta-Ala(4)]-dermorphin (1-4) (TAPA), a highly selective mu(1)-opioid receptor agonist, on mouse gastrointestinal transit was compared with that of morphine and [D-Ala(2), N-methyl-Phe(4), Gly(5)-ol]-enkephalin (DAMGO). When administered intracerebroventricularly 5 min before the oral injection of charcoal meal, TAPA (10-100 pmol), morphine (0.25-4 nmol), and DAMGO (20-80 pmol) dose-dependently inhibited gastrointestinal transit of charcoal. The inhibitory effect of each mu-opioid receptor agonist was completely antagonized by naloxone, a nonselective opioid receptor antagonist. The inhibitory effects of morphine and DAMGO were significantly antagonized by both beta-funaltrexamine, a selective mu-opioid receptor antagonist, and naloxonazine, a selective mu(1)-opioid receptor antagonist. In contrast, the inhibitory effect of TAPA was not affected at all by beta-funaltrexamine, naloxonazine, nor-binaltorphimine (a selective kappa-opioid receptor antagonist), or naltrindole (a selective delta-opioid receptor antagonist). These results suggest that the inhibitory effect of TAPA on gastrointestinal transit may be mediated through an opioid receptor mechanism different from that of morphine and DAMGO.     

Ethylene Production, 1-Aminocyclopropane-l-Carboxylic Acid Content and Its Conversion to Ethylene in Axial Segments of Dormant and Nondormant Cocklebur Seeds

During the imbibition of water, the change in the ethylene productionof axial segments of nondormant (ND) cocklebur (Xanthium pennsylvanicumWallr.) seeds paralleled the change in the content of free 1-aminocyclopropane-l-carboxylicacid (ACC), but not the change in conjugated hydrolysable ACCin the axes. Aminoethoxyvinylglycine, anoxia and a-aminoisobutyricacid inhibited ethylene production, the lattertwo compoundscausing the accumulation of free ACC. Administration of ACCgreatly enhanced ethylene production in the axes. Thus, freeACC seems to be a direct precursor of ethylene production inthe axial tissue of cocklebur seeds. Imbibed dormant (D) axes characterized by inferior ethyleneproduction had less ability to convert exogenously applied ACCto ethylene as compared to ND axes. But, there was little differencebetween the D and ND axes in the endogenous contents of freeand conjugated ACC. This suggests that the inferior ethyleneproduction found in detached D axes is associated with the lowactivity of an ACC-ethylene converting system. (Received December 17, 1982; Accepted April 30, 1983)     

p21 promotes error-free replication-coupled DNA double-strand break repair

p21 is a well-established regulator of cell cycle progression. The role of p21 in DNA repair, however, remains poorly characterized. Here, we describe a critical role of p21 in a replication-coupled DNA double-strand break (DSB) repair that is mechanistically distinct from its cell cycle checkpoint function. We demonstrate that p21-deficient cells exhibit elevated chromatid-type aberrations, including gaps and breaks, dicentrics and radial formations, following exposure to several DSB-inducing agents. p21(-/-) cells also exhibit an increased DNA damage-inducible DNA-PK(CS) S2056 phosphorylation, indicative of elevated non-homologous DNA end joining. Concomitantly, p21(-/-) cells are defective in replication-coupled homologous recombination (HR), exhibiting decreased sister chromatid exchanges and HR-dependent repair as determined using a crosslinked GFP reporter assay. Importantly, we establish that the DSB hypersensitivity of p21(-/-) cells is associated with increased cyclin-dependent kinase (CDK)-dependent BRCA2 S3291 phosphorylation and MRE11 nuclear foci formation and can be rescued by inhibition of CDK or MRE11 nuclease activity. Collectively, our results uncover a novel mechanism by which p21 regulates the fidelity of replication-coupled DSB repair and the maintenance of chromosome stability distinct from its role in the G1-S phase checkpoint.     

Ethylene-Enhanced Transport of 14C-Labeled Metabolites in Rice Seedlings in Relation to Ethylene-Stimulated Coleoptile Growth

To examine the effects of ethylene on sugar transport from endospermsto coleoptiles in rice (Oryza sativa L. cv. Sasanishiki) seedlings,the contents of free sugars in the coleoptiles of explants fedcold glucose and the distributions of ¹⁴C-activities after feedingof ¹⁴C-glucose to the scutella were determined at various timesafter ethylene application. Changes in sucrose, glucose andfructose in the cold glucose-fed explants exposed to ethylenewere similar to those in the ethylene-treated intact seedlingshaving endosperms. Ethylene enhanced the transport of ¹⁴C-labeledmetabolites from the scutella to the coleoptiles. Most of the¹⁴C accumulated in the ethylene-treated coleoptiles were presentas neutral substances in the ethanol-soluble fraction. Regardlessof the presence or absence of ethylene, the incorporation of¹⁴C into sucrose preceded that into glucose and fructose. Theglucose and fructose moieties of ¹⁴C-sucrose in the coleoptileswere almost equally labeled, and the specific activities of¹⁴C-sucrose were higher than those of ¹⁴C-glucose and ¹⁴C-fructose.These results suggested that sucrose synthesized in the scutellawas exported to the coleoptiles, and cleaved there into glucoseand fructose. Ethylene may accelerate the transport of ¹⁴C-labeledmetabolites by activating sucrose cleavage in the coleoptiles. (Received July 1, 1985; Accepted September 17, 1985)     

Thermoperiodism in cocklebur seed germination

Germination potential in nondormant, upper cocklebur (Xanthium pensylvanicum Wallr.) seeds, which were incapable of germinating under constant temperatures below 25 C in air, was increased by exposure to diurnally alternating temperatures. The cocklebur seeds failed to respond to the temperature fluctuations in the beginning of water imbibition, and their responsiveness appeared only after aerobic presoaking for a limited period or after anaerobic pretreatment for 1 to 3 days.

Maximal germination was obtained after exposure to a thermoperiodic regime of 8 hours at 23 C and 16 hours at 8 C. A process occurring during the high temperature phase was aerobic and had to precede the inductive low temperature phase, its effect increasing with temperature. Critical minimum length of the inductive low temperature phase changed with the duration of a preceding anaerobiosis, for instance about 4 hours after 1 day anaerobiosis, but about 2 hours after 2 days. Percentage of subsequent germination was in proportion to the number of thermoperiodic cycles. A process of the inductive low temperature phase was not perturbed by inserting a brief higher temperature period into its phase; indeed, such insertion rather increased germination potential when performed in the earlier parts of the inductive low temperature phase. The effect of the low temperature survived for 13 to 17 hours during the higher temperature period.

     

Engineering analysis of the high-density heterotrophic cultivation of mung bean sprouts

This study investigated the heterotrophic growth behavior of mung beans cultivated in an individual bed under water supply. The fresh weight of mung beans in the bed was estimated, and changes in temperature, and oxygen and carbon dioxide concentrations were recorded during the cultivation period. The specific growth rate, oxygen uptake rate, and carbon dioxide evolution rate, based on the fresh weight in the bed, were calculated. Growth under heterotrophic cultivation can be classified into the following three stages. Reductions in specific oxygen uptake rate, specific carbon dioxide evolution rate, and specific energy production rate corresponded to that of specific growth rate. Indicators of biological activity related to oxygen and carbon dioxide were evaluated quantitatively for beds under high-density heterotrophic cultivation. Moreover, the results obtained from this study successfully demonstrate that there is a relationship between the growth of mung beans and indicators of biological activity.