Changes in the Activity of the Maturation-Promoting Factor Are Correlated with Those of a Major Cyclic AMP and Calcium-Independent Protein Kinase During the First Mitotic Cell Cycles in the Early Starfish Embryo

Many studies suggest that MPF activation depends on protein phosphorylation or that MPF is itself a protein kinase. In the present report, cyclic variations of MPF activity have been correlated in vivo with changes in the extent of protein phosphorylation or in vitro with changes of a major protein kinase during the first cell cycles of fertilized starfish eggs. This cycling protein kinase neither requires cAMP nor Ca²⁺. Neither colchicine nor aphidicoline, which inhibits cleavage and chromosome replication respectively, was found to suppress the synchronous and cyclic variations of both MPF and protein kinase activities. Protein synthesis was found to be required for both MPF and protein kinase activities to reappear after their simultaneous drop at the time of mitotic or meiotic cleavages. Production of either MPF or protein kinase activities is not the immediate result of protein synthesis since there is a delay at each cell cycle between the time when protein synthesis is required and the time when both MPF and protein kinase activities are produced. This suggests that both MPF and protein kinase activities might involve some post-translational modification of a precursor protein synthesized during the preceeding cell cycle.     

A protocol for the purification of bovine serum albumin free of deoxyribonuclease activity

Bovine serum albumin, free of deoxyribonuclease activity, was obtained in our laboratory using ion-exchange chromatography followed by acetylation. Chromatography on four different resins (DEAE-52, P-11, hydroxylapatite and Q Sepharose fast-flow) was examined. Fractions from Q Sepharose chromatography, eluted with a linear gradient 0-1.0 M NaCl and subsequently acetylated, proved to be the most effective method for obtaining deoxyribonuclease-free bovine serum albumin.     

Mechanisms of degradation of 2′-5′ oligoadenylates

We have studied the mechanisms of breakdown of 2'-5' oligoadenylates. We monitored the time-courses of degradation of ppp(A2'p5')nA (dimer to tetramer) and of 5'OH-(A2'p5')nA (dimer to pentamer) in unfractionated L1210 cell extract. The 5' triphosphorylated 2'-5' oligoadenylates are converted by a phosphatase activity. However, 2'-5' oligoadenylates are degraded mainly by phosphodiesterase activity which splits the 2'-5' phosphodiester bond sequentially at the 2' end to yield 5' AMP and one-unit-shorter oligomers. The nonlinear least-squares curve-fitting program CONSAM was used to fit these kinetics and to determine the degradation rate constant of each oligomer. Trimers and tetramers, whether 5' triphosphorylated or not, are degraded at the same rate, whereas 5' triphosphorylated dimer is rapidly hydrolyzed and 5'-OH dimer is the most stable oligomer. The interaction between degradation enzymes and the substrate strongly depends on the presence of a 5' phosphate group in the vicinity of the phosphodiester bond to be hydrolyzed; indeed, when this 5' phosphate group is present, as in pp/pA2'p5'A/or A2'/p5'A2'p5'A/, affinity is high and maximal velocity is low. Such a degradation pattern can control the concentration of 2'-5' oligoadenylates active on RNAse L either by limiting their synthesis (5' triphosphorylated dimer is the primer necessary for the formation of longer oligomers) and/or by converting them into inhibitory (e.g., monophosphorylated trimer) or inactive (e.g., nonphosphorylated oligomers) molecules.     

PCR amplification of chromosome-specific DNA isolated from flow cytometry-sorted chromosomes.

We have established a method for amplifying and obtaining large quantities of chromosome-specific DNA by linker/adaptor ligation and polymerase chain reaction (PCR). Small quantities of DNA isolated from flow cytometry-sorted chromosomes 17 and 21 were digested with MboI, ligated to a linker/adaptor, and then subjected to 35 cycles of PCR. Using this procedure, 20 micrograms of chromosome-specific DNA can be obtained. Southern blot analysis using several DNA probes previously localized to chromosomes 17 and 21 indicated that these gene sequences were present in the amplified chromosome-specific DNA. A small quantity of the chromosome-specific DNA obtained from the first round of PCR amplification was used to amplify DNA for a second, third, and fourth round of PCR (30 cycles), and specific DNA sequences were still detectable. Fluorescence in situ hybridization using these chromosome-specific DNA probes clearly indicated the hybridization signals to the designated chromosomes. We showed that PCR-amplified chromosome 17-specific DNA can be used to detect nonrandom chromosomal translocation of t(15;17) in acute promyelocytic leukemia by fluorescence in situ hybridization.     

中国平脉树螽属五新种记述：直翅目：螽斯科：树螽亚科

本文报道中国平脉树螽属5个新种。每个新种皆有详细的形态描述和形态特征图。所有模式标本存于北京农业大学昆虫标本室。     

The synergistic lethal interaction of cis-diamminedichloroplatinum and natural nucleosides is related to increased DNA cross-links

Human tumor cells were treated in vitro with combinations of cis- or trans-dichlodiammineplatinum (DDP) and natural nucleosides (thymidine, uridine, cytidine and adenosine). Effects were measured by inhibition of colony-formation (cell survival) and DNA alkaline elution (DNA cross-links). No increments in cell lethality or DNA cross-links were elicited by any combination of trans-DDP and nucleosides. In contrast, every combination of cis-DDP and nucleoside was eminently synergistic with 5- and 10-fold increases in cell lethality over the predicted sum of each agent alone. These increments in cell kill correlated linearly with increases in DNA crosslinks suggesting that the nucleosides interact with cis-DDP to enhance its cytotoxic crosslinking mode of action.     

Changes in Abscisic Acid Content in Axis and Cotyledons of Developing Phaseolus vulgaris Embryos and their Physiological Consequences

Prevost, I. and Le Page–Degivry, M. Th. 1985. Changesin absicisic acid content in axis and cotyledons of developingPhaseolus vulgaris embryos and their physiological consequences.—J.exp. Bot. 36: 1900–1905.Changes in abscisic acid (ABA)content with time were measured in embryonic axes and in cotyledonsof Phaseolus vulgaris embryos using a radio–immunoassay.During embryogenesis, a similar pattern was observed in bothtissues: ABA increased to a maximum 29 d after an thesis, followedby a decrease as the seed matured. The level of ABA in the cotyledonswas always much higher than that in the axes. In in vitro cultures,the duration of the lag phase before germination of isolatedembryonic axes increased with ABA content. The presence of cotyledonsalways lengthened the lag phase; longer lag phases were associatedwith greater concentrations of ABA in the cotyledons. Moreoverthe presence of cotyledons stimulated the growth of seedlings. Key words: ABA distribution, embryo maturation, axis and embryo germinability