Macroptilium atropurpureum (siratro) host specificity genes are linked to a nodD-like gene in the broad host range Rhizobium strain NGR234

Summary A 6.7 kb HindIII fragment from the Sym-plasmid of strain NGR234 was found to code a nodD-like gene flanked by two loci which were required for siratro host range. Transfer of the 6.7 kb fragment from NGR234 to R. trifolii strain ANU843 conferred extended host range ability to this strain on siratro plants but not to other plants normally nodulated by strain NGR234. Tn5 mutagenesis of the 6.7 kb fragment showed that insertions located into loci flanking the nodD-like gene abolished the extended host range phenotype. A hybridization probe spanning one of the host specificity loci was shown to hybridize to three specific bands in the NGR234 genome. Complementation and DNA hybridization data showed that the nodD-like gene of strain NGR234 was functionally similar to that in R. trifolii. The introduction to R. trifolii of the 6.7 kb HindIII fragment containing Tn5 insertions located in the nodD-like gene did not abolish the ability to extend the host range of R. trifolii to siratro plants. However, transfer of the 6.7 kb HindIII to R. trifolii derivatives containing Tn5 insertions into either nodA, B or C or other R. trifolii nod genes failed to confer siratro nodulation to these recipients. Reconstruction experiments showed that the 6.7 kb fragment from strain NGR234 and the 14 kb nodulation region of R. trifolii could induce the nodulation of siratro plants when introduced together into Sym-plasmid-cured Rhizobium strains.     

Application of fast atom bombardment mass spectrometry to chlorogenic acids

The technique of positive- and negative-ion fast atom bombardment mass spectrometry has been shown to be capable of producing molecular mass and useful fragmentation information for the structural elucidation of chlorogenic acids. The mass spectra of chlorogenic acid and the related compounds 3′-O-methylchlorogenic acid, neochlorogenic acid, 4,5-dicaffeoyl quinic acid and 1,5-dicaffeoyl quinic acid are compared with those obtained by electron impact mass spectrometry.     

Effects of p,p''-DDT on the Rat Brain Concentrations of Biogenic Amine and Amino Acid Neurotransmitters and Their Association with p,p''-DDT-Induced Tremor and Hyperthermia

Male, Fischer strain 344 adult rats were given various doses (25-100 mg/kg) of p,p'-DDT by oral gavage, and levels of biogenic amines, their metabolites, and amino acid neurotransmitters, tremor activity, and rectal temperature were measured at several intervals (2, 5, 12, and 24 h) after dosing. Dose-related increases in rectal temperature and in tremor activity were observed at 50-100 mg/kg 12 h after dosing. Tremorigenic doses of DDT increased the 5-hydroxyindoleacetic acid (5-HIAA) level in hypothalamus, brainstem, and striatum, whereas doses of 75 and 100 mg/kg increased the 3-methoxy-4-hydroxyphenylglycol (MHPG) level in hypothalamus and brainstem and the 3,4-dihydroxyphenylacetic acid level in striatum. Six amino acids were assayed in the brainstem, hypothalamus, and striatum; aspartate and glutamate levels were increased only in brainstem at 25-100 mg/kg. No consistent changes in concentrations of taurine, glutamine, glycine, or gamma-aminobutyric acid were observed in any of the regions assayed. Time-related increases in rectal temperature were seen 2-12 h after dosing, and the presence of tremor was observed 5-12 h after dosing; for both the time of peak effect was at 12 h. The DDT-induced hyperthermia and tremor were associated with dose- and time-related increases in levels of 5-HIAA, MHPG, aspartate, and glutamate. It is suggested that an increase in the turnover rate of 5-hydroxytryptamine (5-HT) may be responsible for the DDT-induced hyperthermia, whereas increases in the metabolism of 5-HT and norepinephrine may be involved in the tremor.     

Highly potent and specific inhibitors of human renin

We designed aldehyde derivatives of small peptides representing the C-terminal portion of angiotensin I sequence as an inhibitor of human renin. Among compounds that we synthesized, benzyloxycarbonyl (Z)-Phe-His-Leucinal (compound V), Z-Pro-Phe-His-Leucinal (Compound IV) and Z-[3-(1'-naphthyl)Ala]-His-Leucinal (compound VII) markedly inhibited human renin (IC50, 7.5 X 10(-7), 3.2 X 10(-7) and 8.0 X 10(-8) mol/l, respectively). Compound VII was shown to be noncompetitive (Ki = 2.4 X 10(-7) mol/l). It did not inhibit either cathepsin D or pepsin. Compound V had slight or no inhibitory effect at the concentration of 10(-5) mol/l on six animal renins except for monkey and rabbit renins. Results obtained show that these aldehyde compounds are highly selective and species specific inhibitors for human and monkey renins.     

Structural implications of primary sequences from a family of Balbiani ring-encoded proteins inChironomus

Summary DNA sequencing has revealed an internal, tandemly repetitive structure in the family of giant polypeptides encoded by three types of Balbiani ring (BR) genes, in three different species ofChironomus. Each major BR repeat can be subdivided into two halves: a region consisting of short subrepeats and a more constant region that lacks obvious subrepeats. Comparative predictions of secondary structure indicate that an -helical segment is consistently present in the amino-terminal half of the constant region in all known BR proteins. Comparative predictions, coupled with consideration of the known phosphorylation of serine and threonine residues in BR proteins, suggest that the -helical structure may also extend into the carboxy-terminal half of the constant region, possibly interrupted by -turn(s). However, it is also possible that the structure is variable, and that a -strand is present in that half in some cases. All of the constant regions conserve one methionine and one phenylalanine residue, as well as all four cysteines; these residues presumably play roles in the packing or cross-linking of aligned constant regions. The structure of the subrepeat region is not clear, but the prevalence of a tripeptide pattern (basic-proline-acidic) suggests some type of structural regularity, possibly an extended helix. The possible significance of these conserved molecular features is discussed in the context of how they may serve the elasticity, insolubility, and hydrophilicity of the fibrils and threads formed by the BR polypeptides.     

Characterization of chlorophyll fluorescence quenching in chloroplasts by fluorescence spectroscopy at 77 K II. ATP-dependent quenching

In intact, uncoupled type B chloroplasts from spinach, added ATP causes a slow light-induced decline ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{≈ 3}\text{min}$) of chlorophyll a fluorescence at room temperature. Fluorescence spectra were recorded after fast cooling to 77 K and normalized with fluorescein as an internal standard. Related to the fluorescence quenching at room temperature, an increase in Photosystem (PS) I fluorescence (F₇₃₅) and a decrease in PS II fluorescence (F₆₉₅) were observed in the low-temperature spectra. The change in the $\text{F}{}_{735}\text{F}{}_{695}$ ratio was abolished by the presence of methyl viologen. Fluorescence induction at 77 K of chloroplasts frozen in the quenched state showed lowered variable (F_v) and initial (F₀) fluorescence at 690 nm and an increase in F₀ at 735 nm. The results are interpreted as indicating an ATP-dependent change of the initial distribution of excitation energy in favor of PS I, which is controlled by the redox state of the electron-transport chain and, according to current theories, is caused by phosphorylation of the light-harvesting complex.     

The nature of the stable noncovalent dimers of band 3 protein from erythrocyte membranes in solutions of Triton X-100

Stable noncovalent dimers of band 3 protein from human erythrocyte membranes, in which state the protein is thought to exist after solubilization by the nonionic detergent Triton X-100, do not occur when purified batches of the detergent are used. Instead, the protein is in a monomer/dimer/tetramer association equilibrium. The stable dimers do appear, however, when the detergent has been 'aged'. They thus seem to be artifacts.     

The steroids and fatty acids of the basidiomycete Scleroderma polyrhizum

The fruit bodies of the Basidiomycete Scleroderma polyrhizum have been shown to contain the steroids ergosta-4,6,8(14) 22-tetraen-3-one and 5α,8α-epidoxyergosta-6,22-dien-3β-ol and also palmitic and oleic acids.     

Mutations resistant to bromodeoxyuridine in mouse lymphoma cells selected by repeated exposure to EMS characteristics of phenotypic instability and reversion to HAT resistance by 5-azacytidine

Mutations induced by repeated EMS treatments were investigated by using mouse L5178Y cells. The frequency of TG^r mutations increased linearly with the number of EMS treatments whereas the yield of BrdUrd^r mutations showed a curvilinear dose-response curve. The BrdUrd^r frequency was roughly proportional to the square of the TG^r frequency and the results were compatible with the hypothesis that BrdUrd^r cells were induced by two mutational events within a cell. Most of the BrdUrd^r colonies isolated after 6 EMS treatments, however, were unstable. When BrdUrd^r colonies that had arisen in BrdUrd medium after 2 weeks' incubation were isolated in normal medium, the descendant cells showed a nearly normal level of thymidine incorporation and low plating efficiencies of about 1% in BrdUrd medium. In contrast, after isolation of the same colonies in BrdUrd medium, a low level of thymidine incorporation and high plating efficiencies in BrdUrd medium were observed in the descendant cells.

Reverse selection from BrdUrd^r to HAT^r was accomplished with frequencies of 10⁻⁶−10⁻³ for the descendants grown in BrdUrd medium, and AzaCyd treatment drastically increased the reversion frequency to nearly 10⁻¹. Further re-revertants from HAT^r to BrdUrd^r were also found with frequencies of 10⁻³−10⁻² without treatment. These results indicate that the initial BrdUrd^r cells did not result from inactivation of the thymidine-kinase gene but that the mode of gene expression was altered in some way.