Generation of formic acid and ethanolamine from serine in biosynthesis of linear gramicidin by a cell-free preparation of Bacillusbrevis (ATCC 8185)

A growing organism that produces antibiotic peptide was incubated with L-(U-¹⁴C)serine for labeling linear gramicidin. Linear gramicidin was isolated by a simple chromatographic method from tyrothricin (mixture of linear gramicidin and tyrocidine) applied to a column of basic aluminum oxide. The hydrolysate of labeled linear gramicidin on thin layer chromatography showed that L-(U-¹⁴C)serine was one of a precursor of ethanolamine moiety by autoradiography. L-(3-¹⁴C)serine generated formic acid in the presence of tetrahydrofolic acid by an enzyme fraction prepared with ammonium sulfate, and further formed ethanolamine binding to the protein. Formylvaline was biosynthesized by it with tetrahydrofolic acid and ATP, and subsequently released from the protein.     

MIXED MODEL APPROACHES FOR ESTIMATING GENETIC VARIANCES AND COVARIANCES

The limitations of methods for analysis of variance(ANOVA)in estimating genetic variances are discussed. Among the three methods(maximum likelihood ML, restricted maximum likelihood REML, and minimum norm quadratic unbiased estimation MINQUE)for mixed linear models, MINQUE method is presented with formulae for estimating variance components and covariances components and for predicting genetic effects. Several genetic models, which cannot be appropriately analyzed by ANOVA methods, are introduced in forms of mixed linear models. Genetic models with independent random effects can be analyzed by MINQUE(1)method whieh is a MINQUE method with all prior values setting 1. MINQUE(1)method can give unbiased estimation for variance components and covariance components, and linear unbiased prediction (LUP) for genetic effects. There are more complicate genetic models for plant seeds which involve correlated random effects. MINQUE(0/1)method, which is a MINQUE method with all prior covariances setting 0 and all prior variances setting 1, is suitable for estimating variance and covariance components in these models. Mixed model approaches have advantage over ANOVA methods for the capacity of analyzing unbalanced data and complicated models. Some problems about estimation and hypothesis test by MINQUE method are discussed.     

杭州湾六市土地生态环境的数量评价及其在国土规划上的意义

在系统调查分析和特尔斐测定的基础上,选取人口密度、耕地人口负荷量、土地工业经济密度、居民点、厂矿用地、>25°土地面积、单位森林蓄积占用土地、耕地非旱涝保收面积7项指标,应用分值权重累加、系统聚类分析和模糊综合评价3种方法对杭州湾6市土地生态环境作综合分析评价,结果可应用于国土规划实践,对探讨土地生态环境评价的理论与方法有参考价值。     

Resistance to Spodoptera exigua in Apium prostratum

Two Apium accessions were compared with the commercial cultivar Tall Utah 52–70R (A. graveolens [L.]) for resistance to Spodoptera exigua (Hübner)(Lepidoptera: Noctuidae). Oviposition rate was not significantly different between the three genotypes. In all accessions, eggs were usually placed on the upper half of the plants. Implications of this oviposition pattern on S. exigua management in celery are discussed. The wild species A. prostratum ssp prostratum var filiform (A230) showed a significantly higher resistance to S. exigua than 52–70R. The levels of carcinogenic and mutagenic linear furanocoumarins in the commercial cultivar 52–70R (1.41 g/g in the petioles; 5.85 g/g in the leaves) and in the plant accession A. nodiflorum (5.40 g/g in the petioles; 2.99 g/g in the leaves) were far below the concentration reported to produce acute contact dermatitis (18.0 g/g). The levels of furanocoumarins in A. prostratum petioles (186.14 g/g) and leaves (326.45 g/g) were 10 and 18 times higher, respectively, than the concentration known to cause contact dermatitis. However, resistance in A. prostratum was primarily due to non-preference and the linear furanocoumarins did not induce non-preference. Therefore, the resistance shown by this plant accession does not appear to be furanocoumarin-based and may be suitable for transfer to commercial celery for use in S. exigua management.     

On coenzyme Q orientation in membranes: A linear dichroism study of ubiquinones in a model bilayer

Summary A general approach is developed to interpret linear dichroism (LD) spectra of ubiquinones (Q _n) in host bilayers. Information is reported in terms of guest-host mutual orientation and localization. The overall orientational anisotropy of guest ubiquinone molecules is described by a basic set of limiting orientation/localization modes. Assignments of the UV transitions of the ubiquinone chromophore were obtained by the liquid crystal-linear dichroism technique and molecular orbital (CNDO/S) calculations. The LD spectra of Q _n in the bilayers provided by the lyotropic nematic mesophase exhibited by water solutions of potassium laurate and decanol were interpreted on the basis of the above assignments. The resulting experimental evidence showed a multisite distribution in the host bilayer for the aromatic heads of all the investigated Q _n derivatives except Q₀. The orientational distribution suggested by the LD spectra fits the solubilization model recently proposed by G. Lenaz [J. Membrane Biol. (1988) 104:193–209] for ubiquinone in lipid membranes. Within this model Q _n molecules are located in the midplane and their headgroups oscillate transversally across the membrane. Q ₀ instead has a single site location, close to the polar bilayer interface. Experimental evidence that the headgroup carbonyls tend to grasp the polar interface of the host bilayer was also obtained. Orientation and location distributions of Q _n guest molecules are therefore likely to result from the tendency of their aromatic heads to grasp the polar heads of the host bilayer and from the concurrent tendency of their chains to settle into the hydrocarbon host interior.abbreviations AA average absorption - OD, OD optical densities for plane polarized radiations parallel () and perpendicular () to the sample optical axis - OD OD — OD - EPR electron paramagnetic resonance - LC-LD liquid crystal-linear dichroism - LD linear dichroism - LD _r reduced linear dichroism. - MO molecular orbital - N nematic - NMR nuclear magnetic resonance - S _jj order parameters of the directions j of the transition moments of the guest chromophore - S _ii order parameters of the orientational axes i of the guest molecule with respect to the magnetic field - S _ii order parameters of the axes i of the guest molecules with respect to the bilayer axis a - S _a order parameters of the host bilayer axis a with respect to the orienting magnetic field - _j,i deflection angles between the directions j and the axes i - O _i optical factors of the i axis see Eq. (A4)] - Q_n ubiquinone whose isoprenoid chain contains n isoprenoid units Dr. A. Rossi is gratefully acknowledged for the t.e.m. reduction of the spectra. Ubiquinone homologs were kind gifts from Eisai Co., Tokyo, Japan. This work was supported by M.U.R.S.T., and C.N.R. Target Project on Biotechnology and Bioinstrumentation, Rome, Italy.     

Gene conversion in the Escherichia coli RecF pathway: a successive half crossing-over model.

Summary Gene conversion - apparently non-reciprocal transfer of sequence information between homologous DNA sequences - has been reported in various organisms. Frequent association of gene conversion with reciprocal exchange (crossing-over) of the flanking sequences in meiosis has formed the basis of the current view that gene conversion reflects events at the site of interaction during homologous recombination. In order to analyze mechanisms of gene conversion and homologous recombination in an Escherichia coli strain with an active RecF pathway (recBC sbcBC), we first established in cells of this strain a plasmid carrying two mutant neo genes, each deleted for a different gene segment, in inverted orientation. We then selected kanamycin-resistant plasmids that had reconstituted an intact neo ⁺ gene by homologous recombination. We found that all the neo ⁺ plasmids from these clones belonged to the gene-conversion type in the sense that they carried one neo ⁺ gene and retained one of the mutant neo genes. This apparent gene conversion was, however, only very rarely accompanied by apparent crossing-over of the flanking sequences. This is in contrast to the case in a rec ⁺ strain. or in a strain with an active RecE pathway (recBC sbcA). Our further analyses, especially comparisons with apparent gene conversion in the rec ⁺ strain, led us to propose a mechanism for this biased gene conversion. This successive half crossing-over model proposes that the elementary recombinational process is half crossing;-over in the sense that it generates only one recombinant DNA duplex molecule, and leaves one or two free end(s), out of two parental DNA duplexes. The resulting free end is, the model assumes, recombinogenic and frequently engages in a second round of half crossing-over with the recombinant duplex. The products resulting from such interaction involving two molecules of the plasmid would be classified as belonging to the gene-conversion type without crossing-over. We constructed a dimeric molecule that mimics the intermediate form hypothesized in this model and introduced it into cells. Biased gene conversion products were obtained in this reconstruction experiment. The half crossing-over mechanism can also explain formation of huge linear multimers of bacterial plasmids, the nature of transcribable recombination products in bacterial conjugation, chromosomal gene conversion not accompanied by flanking exchange (like that in yeast mating-type switching), and antigenic variation in microorganisms.     

Hückel framework study on the superconducting vibronic interaction in (AB) N chains

Superconducting vibronic interaction in the vibronic superconductivity motif has been studied in the Hückel framework for (AB) _N chain systems. Within the on-site and nearest-neighbor approximation a new vibronic constant, /L, has been introduced, of which the importance has been discussed. The effect of the vibronic operator, , has also been studied. It is also concluded that the size-dependence of the superconducting vibronic interaction also exists in the (AB) _N chain systems.On leave from the Changchun Institute of Applied Chemistry, Academia Sinica, Changchun, P. R. China, as an STA fellowship awardee hosted by the Institute of Physical and Chemical Research of Japan.     

Linear and circular dichroism of membranes from Rhodopseudomonas capsulata

Absorption, linear dichroism and circular dichroism spectra of Rhodopseudomonas capsulata (wild-type-St. Louis strain, mutant Y5 and mutant Ala⁺) are particularly sensitive to the nature of the light-harvesting bacteriochlorophyll-carotenoid-protein complexes. Evidence for exciton-type interactions is seen near 855 nm in the membranes from the wild-type and from mutant Y5, as well as in an isolated B-800 + 850 light-harvesting complex from mutant Y5. The strong circular dichroism that reflects these interactions is attenuated more than 10-fold in membranes from the Ala⁺ mutant, which lacks both B-800 + 850 and colored carotenoids and contains only the B-875 light-harvesting complex. These results lead to the conclusion that these two light-harvesting complexes have significantly different chromophore arrangements or local environments.     

Non-equivalence of YEPD and synthetic complete media in yeast reversion studies

In yeast reversion studies, assay of the total number of cells is made by plating irradiated cells on agar plates containing yeast extract, peptone and dextrose (YEPD) medium. The number of revertants are scored by plating cells on synthetic complete (SC) medium deficient in the particular nutrient for which the reversion is tested. In this procedure equivalence for cell survival between the YEPD and the SC media is always assumed. However it is shown in this paper that this assumption is valid only up to dose levels where cell killing is not significant. At high doses, survivals on the two media differ significantly from each other for both high and low LET radiations. This difference influences the slope of the reversion frequency curve at high doses. Since the reversion frequency is expressed with reference to the number of survivors after a given radiation dose, it is essential to see that the same chance of survival is offered to the reverted and unreverted cells.Even though reversion is reported to vary linearly with dose, it is found that this linearity is restricted only to dose levels where cell killing is not significant. At higher doses, the reversion frequency varies in a very complex manner with dose for both high and low LET radiations. The complexity depends further on the reference medium chosen.