Dis3, implicated in mitotic control, binds directly to Ran and enhances the GEF activity of RCC1.

Using the two-hybrid method, we isolated a Saccharomyces cerevisiae cDNA encoding a protein homologous to Schizosaccharomyces pombe protein Dis3sp, using as bait, human GTPase Ran. The DIS3 gene is essential for viability and complements S.pombe mutant dis3-54 which is defective in mitosis. Although Dis3sc has no homology to RanBP1, it bound directly to Ran and the S.cerevisiae Ran homologue Cnr1, but not to the S.cerevisiae RCC1 homologue Srm1. Upon binding to Ran with a 1:1 molar ratio, Dis3sc enhanced a nucleotide-releasing activity of RCC1 on Ran. In the presence of Dis3sc, the K(m) of RCC1 on Ran decreased by half, while the kcat was unchanged. In vivo, Dis3sp was present as oligomers of M(r) 670-200 kDa as previously reported, and the 200 kDa oligomer of Dis3sp was found to include Spi1 and Pim1, the S.pombe homologues of Ran and RCC1, respectively. Although the biological function of the heterotrimeric oligomer consisting of Dis3, Spi1 and Pim1 is unknown, our results indicate that Dis3 is a component of the RCC1-Ran pathway.     

Uptake of Neutral Red by the Vacuoles of a Green Alga, Micrasterias pinnatifida

Neutral red (NR) in the culture medium entered the vacuolesof a green alga, Micrasterias pinnatifida, at a higher rateat pH 8 than at pH 5. NR remained soluble in vacuoles of cellscultured at pH 5, while it precipitated and formed granulesin cells cultured at pH 8. The vacuoles of cells cultured atpH 8 contained fibrils, but those of cells cultured at pH 5did not. The amount of NR that entered the cells was markedlyreduced by the addition to the medium of nigericin at 10^-5M,monensin at 10^-5M, bafilo-mycin A₁ at 10^-5M, or ammonium chlorideat 50 mM. The formation of NR granules in vacuoles were stronglyinhibited and the disorganization of NR granules were acceleratedby the addition of nigericin at 10^-5M, or bafilomycin A₁ at10^-5M to the culture medium. The possibility is discussed thatNR which enters vacuoles might become positively charged (NRH⁺)by protons brought into vacuoles by proton pumps and that NRH⁺might combine with some negatively charged macromolecules toform aggregates or granules. (Received April 18, 1996; Accepted May 27, 1996)     

Acclimation of Respiratory Properties of Leaves of Spinacia oleracea L., a Sun Species, and of Alocasia macrorrhiza (L.) G. Don., a Shade Species, to Changes in Growth Irradiance

To clarify the way in which the light available for growth affectsrespiration in leaves of sun and shade plants, we examined therespiratory properties of mature leaves of Spinacia oleraceaL., a sun species, and of Alocasia macrorrhiza (L.) G. Don.,a shade species, that had been grown at various irradiances.In leaves of S. oleracea, the respiratory rates, on a dry massbasis, decreased with time during the night, and the higherwas the growth irradiance during the day, the higher was therespiratory rate. The marked decreases in the respiratory rateduring the night were accompanied by decreases in the concentrationof carbohydrates in the leaves. By contrast, the respiratoryrates of leaves of A. macrorrhiza were virtually constant throughoutthe night and the absolute rates were lower than those of S.oleracea even though the absolute value of the concentrationof carbohydrates and its decrease at night resembled to thosein S. oleracea. The maximum activities of respiratory enzymeswere also similar to those in S. oleracea. However, the leavesof A. macrorrhiza contained less soluble protein than thoseof S. oleracea. These results suggest that, in S. oleracea,the concentration of carbohydrates might determine the respiratoryrate while such is not the case in A. macrorrhiza. The lowerrespiratory rates in A. macrorrhiza might be due to a lowerdemand for ATP. (Received November 29, 1995; Accepted February 15, 1996)     

Familial Site-specific Ovarian Cancer Is Linked to BRCA1 on 17q12-21

In a study of nine families with “site-specific” ovarian cancer (criterion: three or more cases of epithelial ovarian cancer and no cases of breast cancer diagnosed at age <50 years) we have obtained evidence of linkage to the breast-ovarian cancer susceptibility gene, BRCA1 on 17q12-21. If the risk of cancer in these families is assumed to be restricted to the ovary, the best estimate of the proportion of families linked to BRCA1 is .78 (95% confidence interval .32–1.0). If predisposition to both breast and ovarian cancer is assumed, the proportion linked is 1.0 (95% confidence interval .46–1.0). The linkage of familial site-specific ovarian cancer to BRCA1 indicates the possibility of predictive testing in such families; however, this is only appropriate in families where the evidence for linkage to BRCA1 is conclusive.     

Formation and decomposition of vacuoles inBotryococcus in relation to the trans-Golgi network

Summary The formation and the decomposition of vacuoles in a member of Xanthophyceae,Botryococcus braunii, were examined by light and electron microscopy. Particles around the nucleus were identified as vacuoles from their stainability with neutral red. These particles disappeared during cell division. They reacted positively in an activity test for acid phosphatase. Electron microscopy revealed the presence of spherical vacuoles around the nucleus. During cell division, these vacuoles seemed to be decomposed by the ER which surrounded the vacuoles. Soon after this decomposition, many immature multivesicular bodies (MVBs) appeared to develop from the trans-Golgi network (TGN) and were pinched off from the TGN. These immature MVBs took up small vesicles in them as they grew into the mature MVBs. Mature MVBs took up and digested the surrounding cytoplasm, fused with one another, and eventually became the vacuoles.Abbreviations MVB multivesicular body - TGN trans-Golgi network     

The use of high-spectral-resolution radiometer data for detection of low chlorophyll concentrations in Lake Kinneret

Chlorophyll distribution in Lake Kinneret was estimated in aperiod of low chlorophyll-a concentrations (3–7 mg m^–3)using remotely sensed data. The data set included high-spectral-resolutionradiometric measurements in the range 400–750 nm, chlorophylland suspended matter concentrations, Secchi disk transparencyand vertical attenuation coefficients at 20 stations. The spectroradiometricdata were used to create the algorithms suitable for quantitativedetermination of chlorophyll content. The present paper presentsexperimental field evidence showing that fluorescence can besuccessfully used for remote monitoring of chlorophyll-a content(with an estimation error <0.5 mg m^–3) in productiveinland waters with a background of variable and relatively highsuspended matter concentration.     

Modes of reproduction in Australian populations of Hypericum perforatum L. (St. John's wort) revealed by DNA fingerprinting and cytological methods.

Hypericum perforatum L. (St. John's wort) is widely used in homeopathic medicine, but has also become a serious weed in Australia and many other countries. Reproduction in H. perforatum was investigated using markers based on restriction fragment length polymorphism (RFLP) and amplified fragment length polymorphism (AFLP). Between two Australian populations, plants displayed 14 polymorphisms from a total of 22 scorable RFLP markers when genomic DNA was probed with M13 bacteriophage, but individuals within each population exhibited identical RFLP fingerprints. Ninety-four percent of the progeny of four crosses made between the two populations exhibited identical fingerprint and ploidy level to the maternal parent, and probably originated apomictically. Seven seedlings with recombinant RFLP or AFLP fingerprints were found from a total of 121 progeny. Both molecular marker techniques detected the same recombinants from a subset of screened progeny. Cytological analysis showed that the seven recombinants comprised three tetraploids (2n = 4x = 32), three hexaploids (2n = 6x = 48), and one aneuploid (2n - 1 = 31), which suggested that the level of normal reduced embryo sacs was only 2.5%. These results are discussed in relation to the management of invasive populations, and the implications for plant breeding and production of St. John's wort for medicinal purposes.     

Remote sensing of chlorophyll in Lake Kinneret using highspectral-resolution radiometer and Landsat TM: spectral features of reflectance and algorithm development

High-resolution reflectance spectra in the range of 400–850nm were obtained from Lake Kinneret during a period when densepopulations of the dinoflagellate Peridinium gatunense dominatedthe phytoplankton. Chlorophyll (Chl) concentrations ranged from5.1 to 185 mg m^–3 and from 2.4 to 187.5 mg m^–3 inthe samples of two independent experiments. The most prominentfeatures of the reflectance spectra were: (i) a wide minimumfrom 400 to 500 nm; (ii) a maximum at 550–570 nm, whichdid not surpass 3% in samples with high Chl concentration (>20mgm^–3), indicating a strong absorption by pigments in thegreen range of the spectrum; (iii) a minimum at 676 nm; thiswas {small tilde}1% and was almost insensitive to variationin Chl concentration >10 mg m^–3; (iv) a maximum reflectanceshowed near 700 nm; its magnitude and position were highly dependenton chlorophyll concentration. High-spectral-resolution datawere used as a guideline for selection of the most suitablespectral bands for chlorophyll remote sensing. Models were devised,based on the calculation of the integrated area above the baselinefrom 670 to 850 nm and the reflectance maximal height withinthis range. Some algorithms already used m previous studieswere tested and showed a plausible degree of accuracy when appliedto the current data base. However, novel models devised in thisstudy improved substantially the accuracy of Chl estimationby remotely sensed data, by reducing the estimation error from>11 to 6.5 mg m^–3 Those models were validated by anindependent data set where Chl concentration ranged over twoorders of magnitude. The use of three relatively narrow spectralbands was sufficient for Chl mapping in Lake Kinneret. Therefore,a relatively simple sensor, measuring only a few bands willbe employed in future applications for Chl monitoring in inlandwaters. Radiometric data were also used to simulate radiancesin the channels of TM Landsat and to find the algorithm forChl assessment. The ratio of channel 4 to channel 3 was usedand enabled Chl estimation with an error of <15mg m^–3This algorithm was employed to map Chl in the entire area ofLake Kinneret with 10 gradations.     

DIVISION APPARATUS OF THE CHLOROPLAST IN NANNOCHLORIS BACILLARIS (CHLOROPHYTA)1

Chloroplast division in Nannochloris bacillaris Naumann (Chlorophyta) was examined by electron microscopy after preparation of samples by freeze-substitution. A pair of belts appeared on the surface of the outer and inner envelope membranes at the middle of the chloroplast. These belts seemed to be constructed of thin fibrils that run parallel to the longitudinal direction of the belts. The outer fibrillar belt increased in width as the constriction of the chloroplast advanced. It appears that the fibrillar belt is the division apparatus of the chloroplast. It encircles the chloroplast and finally divides the chloroplast in two as the diameter of the belt decreases.