114 research outputs found
Atomic mutagenesis of stop codon nucleotides reveals the chemical prerequisites for release factor-mediated peptide release.
Termination of protein synthesis is triggered by the recognition of a stop codon at the ribosomal A site and is mediated by class I release factors (RFs). Whereas in bacteria, RF1 and RF2 promote termination at UAA/UAG and UAA/UGA stop codons, respectively, eukaryotes only depend on one RF (eRF1) to initiate peptide release at all three stop codons. Based on several structural as well as biochemical studies, interactions between mRNA, tRNA, and rRNA have been proposed to be required for stop codon recognition. In this study, the influence of these interactions was investigated by using chemically modified stop codons. Single functional groups within stop codon nucleotides were substituted to weaken or completely eliminate specific interactions between the respective mRNA and RFs. Our findings provide detailed insight into the recognition mode of bacterial and eukaryotic RFs, thereby revealing the chemical groups of nucleotides that define the identity of stop codons and provide the means to discriminate against noncognate stop codons or UGG sense codons
Magnetic moments of the SU(3) decuplet baryons in the chiral quark-soliton model
Magnetic moments of baryons are studied within the chiral quark soliton model
with special emphasis on the decuplet of baryons. The model is used to identify
all symmetry breaking terms proportional to . Sum rules for the
magnetic moments are derived. A ``model-independent'' analysis of the symmetry
breaking terms is performed and finally model calculations are presented, which
show the importance of the rotational corrections for cranking of
the soliton.Comment: 22 pages, RevTex. The final version accepted for publication in Phys.
Rev.
Flavor structure of the octet magnetic moments
We use the chiral quark-soliton model to identify all symmetry breaking terms
linear in and investigate the strange magnetic moment in a
``model-independent'' way. Assuming hedgehog symmetry and employing the
collective quantization, we obtain the most general expression for the
flavor-singlet and flavor-octet magnetic moments in terms of seven independent
parameters. Having fitted these parameters to the experimental magnetic moments
of the octet baryons, we show that the strange magnetic moment turns out to be
positive. The best fit obtained by minimizing assuming 15% theoretical
accuracy yields: .Comment: 10 pages. RevTeX is used. One figure is included. The final version
accepted for publication in Phys. Rev.
Semileptonic decay constants of octet baryons in the chiral quark-soliton model
Based on the recent study of the magnetic moments and axial constants within
the framework of the chiral quark-soliton model, we investigate the baryon
semileptonic decay constants and . Employing the
relations between the diagonal transition matrix elements and off-diagonal ones
in the vector and axial-vector channels, we obtain the ratios of baryon
semileptonic decay constants and . The ratio is also
discussed and found that the value predicted by the present model naturally
lies between that of the Skyrme model and that of the nonrelativistic quark
model. The singlet axial constant can be expressed in terms of the
ratio and in the present model and turns out to be small. The
results are compared with available experimental data and found to be in good
agreement with them. In addition, the induced pseudotensor coupling constants
are calculated, the SU(3) symmetry breaking being considered. The
results indicate that the effect of SU(3) symmetry breaking might play an
important role for some decay modes in hyperon semileptonic decay.Comment: 16 pages, RevTeX is used. No figure. Accepted for publication in
Phys. Rev.
Vector transition form factors of the and in the SU(3) chiral quark-soliton model
We investigate the vector transition form factors of the nucleon and vector
meson K^* to the pentaquark baryon Theta^+ within the framework of the SU(3)
chiral quark-soliton model. We take into account the rotational 1/N_c and
linear corrections, assuming isospin symmetry and employing the
symmetry-conserving quantization. It turns out that the leading-order
contributions to the form factors are almost cancelled by the rotational
corrections. Because of this, the flavor SU(3) symmetry-breaking terms yield
sizeable effects on the vector transition form factors. In particular, the main
contribution to the electric-like transition form factor comes from the
wave-function corrections, which is a consequence of the generalized
Ademollo-Gatto theorem derived in the present work. We estimate with the help
of the vector meson dominance the K^* vector and tensor coupling constants for
the Theta^+: and .
We argue that the outcome of the present work is consistent with the null
results of the CLAS experiments in the reactions gamma n -> K^- Theta^+ and
gamma p ->bar{K}^0 Theta^+. The results of the present work are also consistent
with the recent experiments at KEK. In addition, we present the results of the
transition form factors and its
coupling constants.Comment: 26 pages, 10 figure
Differences and Similarities in Predictors of Externalizing Behavior Problems Between Boys and Girls: A 1-Year Follow-Up Study
The aim of this study was to investigate the sex-specific predictive
value of age of onset of delinquent behaviors, callous-unemotional (CU)
traits, and anger-irritability problems for externalizing behavior
problems in institutionalized adolescents over the course of 1 year. A
total of 118 girls and 240 boys from child welfare and juvenile justice
institutions were evaluated twice: At T1, age of onset, CU traits,
anger-irritability problems, nonverbal reasoning, and externalizing
behavior problems were measured; at T2 (later), externalizing behavior
problems were measured a second time. Results showed significant
interactions between sex and anger-irritability problems, and between
sex and CU traits, in the sense that the relation between these two
predictors at T1 and externalizing behavior problems at T2 was stronger
in girls than in boys. Results of this study point out sex differences
in the validity of predictors of externalizing behavior problems
Effective Weak Chiral Lagrangian to in the Chiral Quark Model
We investigate the effective weak chiral Lagrangian within
the framework of the chiral quark model. Starting from the effective four-quark
operators, we derive the effective weak chiral action by integrating out the
constituent quark fields. Employing the derivative expansion, we obtain the
effective weak chiral Lagrangian to order . We examine the
contributions of the order to the ratio
, considering e.g. the quark axial-vector
constant different from unity. The low energy constants of the
counterterms are also presented and discussed.Comment: 25 pages. RevTex is used. 3 postscript figures. Final version for
publication in Nucl. Phys.
A common variant of the MACC1 gene is significantly associated with overall survival in colorectal cancer patients
<p>Abstract</p> <p>Background</p> <p>The newly discovered metastasis-associated in colon cancer-1 (MACC1) gene is a key regulator of the HGF/MET pathway. Deregulation of HGF/MET signaling is reported as a prognostic marker for tumorigenesis, early stage invasion, and metastasis. High expression levels of MACC1 have been associated with colon cancer metastasis and reduced survival. Potential links between the genetic diversity of the MACC1 locus and overall survival are unknown. We therefore investigated the association between MACC1 tagging single nucleotide polymorphisms (SNPs) and overall survival in a large cohort of colorectal cancer patients.</p> <p>Methods</p> <p>The study included 318 subjects with histopathologically proven colorectal cancer at the Academic Teaching Hospital Feldkirch, Austria. Survival data were provided by the federal agency for statistics in Austria. Genomic DNA was isolated from formalin-fixed paraffin-embedded specimens; six tagging SNPs (rs1990172, rs3114446, rs10275612, rs3095007, rs3095009, and rs7780032), capturing most of the common variants of the MACC1 locus, were genotyped by SNaPshot assays.</p> <p>Results</p> <p>Over a mean follow up period of 5.3 (± 1.0) years, 94 deaths were recorded. Carriers of the G-allele of SNP rs1990172 showed a significantly decreased overall survival (additive HR = 1.38 [1.05-1.82]; <it>p </it>= 0.023). Multivariate analysis adjusted for age and UICC tumor stage confirmed this result (HR = 1.49 [1.12-1.98]; <it>p </it>= 0.007). Other investigated genetic variants of the MACC1 gene were not significantly associated with overall survival (<it>p</it>-values > 0.05).</p> <p>Conclusions</p> <p>For the first time, our study investigated the influence of MACC1 tagging polymorphisms on overall survival suggesting SNP rs1990172 as a predictor for reduced overall survival in colorectal cancer patients. Further studies will be required to validate our findings.</p
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