1,215 research outputs found
Enzymes from Fungal and Plant Origin Required for Chemical Diversification of Insecticidal Loline Alkaloids in Grass-\u3cem\u3eEpichloë\u3c/em\u3e Symbiota
The lolines are a class of bioprotective alkaloids that are produced by Epichloë species, fungal endophytes of grasses. These alkaloids are saturated 1-aminopyrrolizidines with a C2 to C7 ether bridge, and are structurally differentiated by the various modifications of the 1-amino group: -NH2 (norloline), -NHCH3 (loline), -N(CH3)2 (N-methylloline), -N(CH3)Ac (N-acetylloline), -NHAc (N-acetylnorloline), and -N(CH3)CHO (N-formylloline). Other than the LolP cytochrome P450, which is required for conversion of N-methylloline to N-formylloline, the enzymatic steps for loline diversification have not yet been established. Through isotopic labeling, we determined that N-acetylnorloline is the first fully cyclized loline alkaloid, implying that deacetylation, methylation, and acetylation steps are all involved in loline alkaloid diversification. Two genes of the loline alkaloid biosynthesis (LOL) gene cluster, lolN and lolM, were predicted to encode an N-acetamidase (deacetylase) and a methyltransferase, respectively. A knockout strain lacking both lolN and lolM stopped the biosynthesis at N-acetylnorloline, and complementation with the two wild-type genes restored production of N-formylloline and N-acetylloline. These results indicated that lolN and lolM are required in the steps from N-acetylnorloline to other lolines. The function of LolM as an N-methyltransferase was confirmed by its heterologous expression in yeast resulting in conversion of norloline to loline, and of loline to N-methylloline. One of the more abundant lolines, N-acetylloline, was observed in some but not all plants with symbiotic Epichloë siegelii, and when provided with exogenous loline, asymbiotic meadow fescue (Lolium pratense) plants produced N-acetylloline, suggesting that a plant acetyltransferase catalyzes N-acetylloline formation. We conclude that although most loline alkaloid biosynthesis reactions are catalyzed by fungal enzymes, both fungal and plant enzymes are responsible for the chemical diversification steps in symbio
Civil conflict, federalism and strategic delegation of leadership
This article analyzes negative externalities that policymakers in one region or group may impose upon the citizens of neighboring regions or groups. These externalities may be material, but they may also be psychological (in the form of envy). The latter form of externality may arise from the production of 'conspicuous' public goods. As a result, decentralized provision of conspicuous public goods may be too high. Potentially, a centralized legislature may internalize negative externalities. However, in a model with strategic delegation, we argue that the median voter in each jurisdiction may anticipate a reduction in local public goods supply and delegate to a policymaker who cares more for public goods than she does herself. This last effect mitigates the expected benefits of policy centralization. The authors' theory is then applied to the setting of civil conflict, where they discuss electoral outcomes in Northern Ireland and Yugoslavia before and after significant institutional changes that affected the degree of centralization. These case studies provide support for the authors' theoretical predictions
Exploring CP Violation through Correlations in B --> pi K, B_d --> pi^+pi^-, B_s --> K^+K^- Observable Space
We investigate allowed regions in observable space of B --> pi K, B_d -->
pi^+pi^- and B_s --> K^+K^- decays, characterizing these modes in the Standard
Model. After a discussion of a new kind of contour plots for the
system, we focus on the mixing- induced and direct CP asymmetries of the decays
B_d --> pi^+pi^- and B_s--> K^+K^-. Using experimental information on the
CP-averaged B_d --> pi^{+/-}K^{+/-} and B_d --> pi^+pi^- branching ratios, the
relevant hadronic penguin parameters can be constrained,implying certain
allowed regions in observable space. In the case of B_d --> pi^+pi^-, an
interesting situation arises now in view of the recent B-factory measurements
of CP violation in this channel, allowing us to obtain new constraints on the
CKM angle gamma as a function of the B^0_d--\bar{B^0_d} mixing phase
phi_d=2beta, which is fixed through A_{CP}^{mix}(B_d --> J/psi K_S) up to a
twofold ambiguity. If we assume that A_{CP}^{mix}(B_d --> pi^+pi^-) is
positive, as indicated by recent Belle data, and that phi_d is in agreement
with the ``indirect'' fits of the unitarity triangle, also the corresponding
values for gamma around 60 degrees can be accommodated. On the other hand, for
the second solution of phi_d, we obtain a gap around gamma ~ 60 degrees. The
allowed region in the space of A_{CP}^{mix}(B_s --> K^+K^-) and
A_{CP}^{dir}(B_s --> K^+K^-) is very constrained in the Standard Model, thereby
providing a narrow target range for run II of the Tevatron and the experiments
of the LHC era.Comment: 34 pages, LaTeX, 12 figures. More detailed introduction and a few
Comments added, conclusions unchanged. To appear in Phys. Rev.
CP violating polarizations in semileptonic heavy meson decays
We study the -violating lepton transverse polarization () in
three body semileptonic heavy meson decays to pseudoscalar mesons and to vector
mesons. We calculate these polarizations in the heavy quark effective limit,
which simplifies the expressions considerably. After examining constraints from
conserving (including ) and violating
processes, we find that in decays, of the muon in multi-Higgs
doublet models can be of order , while of the can even
approach unity. In contrast, in decays is at most 1.5\%. We
discuss possibilities for detection of at current and future
factories. We also show that in decays to vector mesons, unlike in
decays to pseudoscalars, can get contributions from left-right models.
Unfortunately, in that case is proportional to - mixing,
and is thus small.Comment: 32pp plain LATEX, 3 figs (by EMAIL request), TRI-PP-94-1
Bostonia: The Boston University Alumni Magazine. Volume 11
Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs
Ether Bridge Formation in Loline Alkaloid Biosynthesis
Lolines are potent insecticidal agents produced by endophytic fungi of cool-season grasses. These alkaloids are composed of a pyrrolizidine ring system and an uncommon ether bridge linking carbons 2 and 7. Previous results indicated that 1-aminopyrrolizidine was a pathway intermediate. We used RNA interference to knock down expression of lolO, resulting in the accumulation of an alkaloid identified as exo-1-acetamidopyrrolizidine based on high-resolution MS and NMR. Genomes of endophytes differing in alkaloid profiles were sequenced, revealing that those with mutated lolO accumulated exo-1-acetamidopyrrolizidine but no lolines. Heterologous expression of wild-type lolO complemented a lolO mutant, resulting in the production of N-acetylnorloline. These results indicated that the non-heme iron oxygenase, LolO, is required for ether bridge formation, probably through oxidation of exo-1-acetamidopyrrolizidine
Bostonia: The Boston University Alumni Magazine. Volume 12
Founded in 1900, Bostonia magazine is Boston University’s main alumni publication
Towards Extractions of the CKM Angle from and Untagged Decays
The decays and provide interesting
constraints on the angle of the unitarity triangle of the CKM matrix.
It is shown that bounds on can also be obtained from the time
evolution of untagged and decays,
provided the system exhibits a sizeable width difference
. A detailed discussion of rescattering processes and
electroweak penguin effects, which limit the theoretical accuracy of these
constraints, and of methods to control them through experimental data is given.
Moreover, strategies are pointed out to go beyond these bounds by relating the
and untagged decays through the SU(3)
flavour symmetry of strong interactions. If a tagged, time-dependent
measurement of the and modes should
become possible, could be determined from the corresponding
observables in a way that makes use of only the SU(2) isospin symmetry and
takes into account rescattering effects ``automatically''. The impact of
new-physics contributions to mixing is also analysed, and
interesting features arising in such a scenario of physics beyond the Standard
Model are pointed out.Comment: 34 pages, LaTeX, 12 figures, extended version including a detailed
discussion of rescattering and electroweak penguin effect
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