Growth analysis ofQuercus serrata seedlings withinMiscanthus sinensis grass canopies differing in light availability

The effects of different light regimes on the survival, growth and morphology ofQuercus serrata seedlings were studied in canopies ofMiscanthus sinensis. The seedlings of various ages (0–3 yr) were grown in three light regimes: under a denseM. sinensis canopy (TG plot) receiving 2.5%–8.7% of full sunlight, under a relatively sparse canopy (SG plot) receiving 3.8%–16.1% of light and in an adjacent open site (NG plot). There was a little difference in the survival ofQ. serrata seedlings among the three plots. Height and diameter of stem and total leaf area of the seedlings were significantly lower in the shadier plots. However, the first (bottom) flush of the stem was significantly longer in the TG plot than in the NG and SG plots. Total dry weights of individual 1- and 2-yr-oldQ. serrata seedlings in the TG plot were reduced to about one-twelfth of those in the NG plot. Although the relative proportion in dry weight of each organ did not differ significantly among the plots, leaf area ratio, specific leaf area and stem height per unit dry weight were significantly higher in shadier plots. The leaf area per unit stem height was increased considerably in the sunnier plots.     

Search for the optimal sequence of the ribosome binding site by random oligonucleotide-directed mutagenesis.

Synthetic DNA duplexes corresponding to the ribosome binding site (RBS) were synthesized through the phosphite method on solid support. The synthetic RBS DNA with partial random sequences was inserted into an appropriate site between the lpp-lac promoter and the beta-galactosidase structural gene in plasmid pMKT2. The level of beta-galactosidase expression was correlated with the color intensity of the recombinant colonies on X-gal plates. The bluest colonies were isolated and characterized with respect to beta-galactosidase enzyme activity and RBS sequence. There was good correlation between color intensity and the level of the enzyme activity, and this provided a reliable phenotypic screening method in the search for the optimal regulatory sequences. Novel RBS sequences obtained here show not only the unique nucleotide distribution, but also strong complemetarity to the 3' end region of 16S rRNA, from which could be deduced a generalized RBS sequence, the position of the SD region, and the 16S rRNA position mediated during translation initiation.     

Acetic acid production from whey lactose by the co-culture ofStreptococcus lactis andClostridium formicoaceticum

Summary Acetic acid was produced from anaerobic fermentation of lactose by the co-culture ofStreptococcus lactis andClostridium formicoaceticum at 35° C and pHs between 7.0 and 7.6. Lactose was converted to lactic acid, and then to acetic acid in this mixed culture fermentation. The overall acetic acid yield from lactose was about 95% at pH 7.6 and 90% at pH 7.0. The fermentation rate was also higher at pH 7.6 than at pH 7.0. In batch fermentation of whey permeate containing about 5% lactose at pH 7.6, the concentration of acetic acid reached 20 g/l within 20 h. The production rate then became very slow due to end-product inhibition and high Na⁺ concentration. About 30 g/l acetate and 20 g/l lactate were obtained at a fermentation time of 80 h. However, when diluted whey permeate containing 2.5% lactose was used, all the whey lactose was converted to acetic acid within 30 h by this mixed culture.     

柞蚕抗菌肽D中精氨酸、赖氨酸和色氨酸等氨基酸残基的化学修饰

用不同的化学试剂修饰了柞蚕抗菌肽D分子中的色氨酸、精氨酸和赖氨酸等氨基酸残基。NBS修饰抗菌肽D,以及氨肽酶M对抗菌肽D作用的结果表明色氨酸残基对抗菌肽D抑制E.coli D31的作用影响不大。CHD和MLH对精氨酸和赖氨酸残基的修饰,导致抗菌肽D失去抑制E.coli的作用,但可逆地消除CHD和MLH的修饰作用后,抗菌肽D恢复了对E.coli D31的抑菌作用。这些结果初步认为,抗菌肽D抑菌作用与分子中的荷电性有关,改变了分子的电荷,也就同时失去了其抑菌功能。 此外,对精氨酸残基修饰的结果还表明,抗菌肽D的免疫原性与精氨酸残基有关。但是,抗菌肽D的免疫决定簇与其生物活性中心并不完全平行。     

Mutational spectrum and recombinogenic effects induced by aminofluorene adducts in bacteriophage M13

Double-stranded replicative form (RFI) DNA of bacteriophage M13 strain M13mp10 which carries partial lacZ gene has been modified in vitro to various extents with N-hydroxy-2-amino-fluorene (N-OH-AF) and then transfected into E. coli cells. High-performance liquid chromatography (HPLC) analysis results demonstrate that the sole adduct (95%) formed in modified DNA is N-(deoxyguanosine-8-yl)-2-aminofluorene (dG-C8-AF). Approximately 20 adducts per RFI molecule constitute 1 lethal event when plaque-forming ability is assayed on E. coli cells which have received no prior SOS induction. The mutagenicity of dG-C8-AF adducts was assayed by measuring loss of beta-galactosidase activity as a function of adducts per molecule. A dose-dependent increase in Lac- mutants was observed, with a 4-fold increase in mutants per survivor at 30 adducts/molecule. The mutations produced, characterized by DNA sequencing, occur predominantly at either G or C positions different from those observed in the spontaneous mutant spectrum. Restriction-mapping results show that in our assay system, dG-C8-AF adducts induce a previously unreported recombinogenic activity.     

A map of photolytic and tryptic cleavage sites on the beta heavy chain of dynein ATPase from sea urchin sperm flagella

NH2-terminal analysis of the alpha and beta heavy chain polypeptides (Mr greater than 400,000) from the outer arm dynein of sea urchin sperm flagella, compared with that of the 230,000- and 200,000-Mr peptides formed upon photocleavage of dynein by irradiation at 365 nm in the presence of vanadate and ATP, shows that the NH2 termini of the intact chains are acetylated and that the 230,000- and 200,000 Mr peptides constitute the amino- and carboxy-terminal portions of the heavy chains, respectively. Tryptic digestion of the beta heavy chain is known to separate it into two particles, termed fragments A and B, that sediment at 12S and 6S (Ow, R. A., W.-J. Y. Tang, G. Mocz, and I. R. Gibbons, 1987. J. Biol. Chem. 262:3409-3414). Immunoblots against monoclonal antibodies specific for epitopes on the beta heavy chain, used in conjunction with photoaffinity labeling, show that the ATPase-containing fragment A is derived from the amino-terminal region of the beta chain, with the two photolytic sites thought to be associated with the purine-binding and the gamma-phosphate-binding areas of the ATP-binding site spanning an approximately 100,000 Mr region near the middle of the intact beta chain. Fragment B is derived from the complementary carboxy-terminal region of the beta chain.     

Epitopes of an influenza viral peptide recognized by antibody at single amino acid resolution

Antibodies raised against the synthetic peptide corresponding to the carboxy-terminal 24 amino acids (305-328) of the heavy chain of the hemagglutinin molecule of influenza virus A/X-31 (H3) bind this peptide at three antigenic sites. These sites were identified by assaying binding of polyclonal BALB/c mouse antipeptide sera to the complete set of all possible di-, tri, tetra-, penta-, hexa-, hepta-, and octapeptides homologous with the 24-residue sequence. Individual epitopes were defined and essential residues identified by testing the binding of monoclonal antibodies to sets of peptide analogues in which every one of the homologous residues was replaced in turn by each of the 19 alternative genetically coded amino acids. The immunodominant epitope was shown to be a linear sequence of five amino acids, 314LKLAT318. Replacement of any one of these residues with any other amino acid resulted in loss of antibody binding, indicating that all five are essential to the interaction and that they are probably contact residues. Another antigenic site contains at least two overlapping epitopes: polyclonal sera recognize predominantly an epitope or epitopes encompassed by the linear sequence 320MRNVPEKQT328, whereas the epitope defined by a particular monoclonal antibody comprises the seven amino acids 322NVPEKQT328, of which N322, E325, and Q327 were implicated as contact residues.     

Genetic organization and nucleotide sequence of the stability locus of IncFII plasmid NR1

The stability (stb) locus of IncFII plasmid NR1 was mapped to a 1700 base-pair NaeI-TaqI restriction fragment. A series of unstable plasmids that contained insertion, deletion, and point mutations that inactivated the stability function was isolated. The unstable point mutants examined were all stabilized (complemented) in trans by a copy of the wild-type stb locus, suggesting that the mutations had inactivated diffusible gene products. The nucleotide sequence of the stb locus contained two tandem open reading frames, designated stbA and stbB, that encoded essential trans-acting protein products with predicted sizes of 36,000 Mr and 13,000 Mr, respectively. A third open reading frame, stbC, that could encode a peptide of 8000 Mr was contained within stbB in the complementary DNA strand. Plasmid-encoded proteins of 36,000 Mr and 13,000 Mr were identified in minicell experiments as the products of stbA and stbB, respectively. Unstable deletion mutants that retained the promoter proximal region of the stb locus upstream from stbA but had deleted both stbA and stbB were stabilized in trans by plasmids that could supply StbA and StbB. In contrast, deletion mutants that had lost the stbAB promoter region were not complemented in trans, indicating that this region contained an essential cis-acting site (or sites). Unlike some other loci that mediate stable plasmid inheritance, cloned copies of the wild-type stb locus of NR1 did not exert strong incompatibility (i.e. trans destabilization) against other stb+ derivatives of plasmid NR1 present in the same cell.