Structure of branched poly-α-amino acids in dimethylformamide. I. Light scattering

Light scattering of multichain poly-α-amino acids was studied in dimethylformamide (DMF). The polymers consisted of a backbone of poly-L -lysine of degree of polymerization n with side chains of benzyl L -glutamate and benzyl L -aspartate of degree of polymerization, m, on each ε-amino group. The backbone length n is known and m is obtained by amino acid analysis. The results on a series of such materials confirm this structure and show that the molecules are dissolved in highly compacted conformations. It was found that DMF is a poor solvent for these polymers. In the case of the higher molecular weight polymers, the solutions initially were not molecularly disperse. The aggregates were resistant to dilution in the experimental range. Mild heat treatment, however, disaggregated the solutions irreversibly, and the light-scattering data indicated that a structural rearrangement of the molecules had occurred.     

Seismic communication in the blind subterranean mole-rat: patterns of head thumping and of their detection in the Spalax ehrenbergi superspecies in Israel

Patterns of seismic communication and somatosensory responses were studied in four chromosomal species (2n= 52, 54, 58, 60) of blind subterranean mole-rats, belonging to the Spalax ehrenbergi superspecies in Israel. The patterns involved head thumping signals and surface-recorded cerebral potentials evoked by vibrational signals. The patterns correspond to the differences in territory size and population density which characterize the four species. It is suggested that this correspondence is related to the adaptive significance of the seismic communication.     

Immunologically distinct binding molecules for progesterone and RU38486 in the chick oviduct cytosol

[3H]Progesterone and [3H]RU38486 binding in the chick oviduct cytosol is associated with macromolecules which sediment as 8 S and 4 S moieties, respectively, in molybdate-containing 5-20% sucrose gradients. The [3H]progesterone binding could be displaced by excess progesterone, but not by RU38486. Conversely, the [3H]RU38486 binding was able to compete with RU38486 but not by excess progesterone. A preparation containing antibodies against chick oviduct progesterone receptor recognized only the [3H]progesterone-receptor complex but not the 4 S, [3H]RU38486 binding component of the chick cytosol. In the calf uterus cytosol, [3H]R5020 (a synthetic progestin) and [3H]RU38486 were associated with 8 S molecules and the peaks of radioactivity were displaceable upon preincubation with radionert steroids. In addition, the complexes were recognized by antibodies to chick oviduct progesterone receptor. Our data suggest that in the chick oviduct cytosol, RU38486 does not bind to progesterone receptor, but interacts with an immunologically distinct macromolecule.     

Persistence of [14C] gibberellin A3 and [3H] gibberellin A1 in senescing,ethylene treated Citrus and tomato fruit

The fate of [¹⁴C] gibberellin A₃ and [³H] gibberellin A₁ was examined in senescing fruit of Shamouti orange (Citrus sinensis L. Osbeck) and tomato (Lycopersicon esculentum Mill.). Gibberellin A₃ was highly persistent in Citrus peel (t 1/2=18 days) and to a lesser degree in tomato (t 1/2=5.5 days). Ethylene and ethephon caused a slight enhancement of gibberellin A₃ metabolism in Citrus and tomato fruit, respectively. Gibberellin A₁ was metabolized by Citrus peel at a relatively high rate (t 1/2 < 24 h) and ethylene slightly reduced this rate. It is concluded that the ethylene-induced enhancement of senescence does not involve major effects on the deactivation of applied gibberellins.Abbreviations GA₃ gibberellin A₃ - GA₁ gibberellin A₁     

Endogenous abscisic acid and 2-trans-abscisic acid in alternate bearing ‘Wilking’ mandarin trees

The relationship of abscisic acid (ABA) and 2-trans-abscisic acid (t-ABA) to alternate bearing has been examined in Wilking mandarin (Citrus reticulata Blanco) trees. Leaves, stems and buds of trees loaded with fruit (on trees) had 4.3, 6.0 and 2.2 fold higher ABA levels than the corresponding organs from off trees. Leaves had higher ABA levels than stems and buds in both on and off trees. t-ABA was non-detectable in Wilking leaf, stem and bud tissue. Amounts of t-ABA not exceeding 40% of the ABA content, were found in Shamouti and Valencia orange buds and in Wilking fruit peel.The elevated levels of ABA in on tree organs may reflect a stress imposed by the fruit overload.     

Interpretation of the dose and LET dependence of RBE values for lethal lesions in yeast cells

Survival data on yeast cells proficient or deficient in the repair of DNA double-strand breaks (dsb) and data on the induction of dsb are used to interpret the dose dependence of the RBE value for lethal lesions after irradiation at high dose rate followed by 72-hr liquid holding providing optimum conditions for repair of potentially lethal lesions (RBEDP, DP = delayed plating). The radiations applied are conventional (150 kV), soft (50 kV), and ultrasoft (4 kV) X rays, 30-MeV electrons (or 60Co gamma rays), and 3.5-MeV alpha particles. Analysis shows that the dose dependence of the RBEDP value can be explained by the combination of two dose-independent RBE values, one for the single-particle traversal effect (RBEspt) and the other for the accumulation of dsb (RBEdsb) due to the traversal of more than one particle through the cell nucleus. Furthermore, it is shown that the LET dependence of RBEspt values describing the linear component of the lethal lesions must be considered separately for "electron" and "particle" radiations.     

Heterochromatin markers: Arrangement of obligatory heterochromatin,histone genes and multisite gene families in the interphase nucleus of D. melanogaster

Localization, as detected by in situ hybridization, of major heterochromatic blocks in interphase nuclei of larval brain and imaginal discs is reported. We conclude that the position of heterochromatic regions in interphase nuclei is correlated with their respective position in metaphase chromosomes and hence, independent of sequence recognition. Furthermore, chromocentral associations of X-, Y- or autosomal-based heterochromatin are not formed in these cells. Homologues do align in close proximity, but heterochromatin plays no role in this arrangement. Heterochromatin, and probably nucleoli, establish their membrane links in situ, and have no prefixed recognition sites. The most intimate association between homologous repetitive sequences was found in the histone locus, but no tendency for clustering was found among loci of multisite euchromatic gene families.     

Characterization of Semisynthetic and Naturally Nα-Acetylated α-Synuclein in Vitro and in Intact Cells: IMPLICATIONS FOR AGGREGATION AND CELLULAR PROPERTIES OF α-SYNUCLEIN

N-terminal acetylation is a very common post-translational modification, although its role in regulating protein physical properties and function remains poorly understood. α-Synuclein (α-syn), a protein that has been linked to the pathogenesis of Parkinson disease, is constitutively N(α)-acetylated in vivo. Nevertheless, most of the biochemical and biophysical studies on the structure, aggregation, and function of α-syn in vitro utilize recombinant α-syn from Escherichia coli, which is not N-terminally acetylated. To elucidate the effect of N(α)-acetylation on the biophysical and biological properties of α-syn, we produced N(α)-acetylated α-syn first using a semisynthetic methodology based on expressed protein ligation (Berrade, L., and Camarero, J. A. (2009) Cell. Mol. Life Sci. 66, 3909-3922) and then a recombinant expression strategy, to compare its properties to unacetylated α-syn. We demonstrate that both WT and N(α)-acetylated α-syn share a similar secondary structure and oligomeric state using both purified protein preparations and in-cell NMR on E. coli overexpressing N(α)-acetylated α-syn. The two proteins have very close aggregation propensities as shown by thioflavin T binding and sedimentation assays. Furthermore, both N(α)-acetylated and WT α-syn exhibited similar ability to bind synaptosomal membranes in vitro and in HeLa cells, where both internalized proteins exhibited prominent cytosolic subcellular distribution. We then determined the effect of attenuating N(α)-acetylation in living cells, first by using a nonacetylable mutant and then by silencing the enzyme responsible for α-syn N(α)-acetylation. Both approaches revealed similar subcellular distribution and membrane binding for both the nonacetylable mutant and WT α-syn, suggesting that N-terminal acetylation does not significantly affect its structure in vitro and in intact cells.     

Diurnal Patterns of Flight Activity and Effects of Light on Host Finding Behavior of the Asian Citrus Psyllid

The Asian citrus psyllid, Diaphorina citri (Hemiptera: Psyllidae), is an invasive pest of citrus in the United States. The psyllid feeds and reproduces primarily on new flush growth of citrus and other rutaceous plants. Because it vectors the bacterial causal agents of the deadly citrus greening disease, D. citri is potentially a pest of economic importance in all citrus growing areas where it occurs together with the disease. We investigated the diurnal patterns of its flight activity in the field and the effects of light on its host selection and egg laying behaviors. The numbers of adult psyllids caught on yellow sticky traps were 3 to 4-fold higher during daytime than nighttime. Daytime flight activity of D. citri adults also varied with time of the day with peak catches occurring at midday from 1200 to 1500 h. Illumination of the traps at night increased their attractiveness to adult psyllids by 5-fold. Similarly, light significantly increased plant colonization by adults and female egg deposition on potted plants in the laboratory. These results showed that the flight activity and host selection behavior of adult psyllids are regulated by light and circadian rhythms. Thus, adult psyllids utilize light as visual cues in their host-plant selection process.