1,011 research outputs found
Identification of the ribosome binding sites of translation initiation factor IF3 by multidimensional heteronuclear NMR spectroscopy
Titrations of Escherichia coli translation initiation factor IF3, isotopically labeled with 15N, with 30S ribosomal subunits
were followed by NMR by recording two-dimensional (15N,1H)-HSQC spectra. In the titrations, intensity changes
are observed for cross peaks belonging to amides of individual amino acids. At low concentrations of ribosomal
subunits, only resonances belonging to amino acids of the C-domain of IF3 are affected, whereas all those attributed
to the N-domain are still visible. Upon addition of a larger amount of 30S subunits cross peaks belonging to residues
of the N-terminal domain of the protein are also selectively affected.
Our results demonstrate that the two domains of IF3 are functionally independent, each interacting with a different
affinity with the ribosomal subunits, thus allowing the identification of the individual residues of the two domains
involved in this interaction. Overall, the C-domain interacts with the 30S subunits primarily through some of its loops
and a-helices and the residues involved in ribosome binding are distributed rather symmetrically over a fairly large
surface of the domain, while the N-domain interacts mainly via a small number of residues distributed asymmetrically
in this domain.
The spatial organization of the active sites of IF3, emerging through the comparison of the present data with the
previous chemical modification and mutagenesis data, is discussed in light of the ribosomal localization of IF3 and
of the mechanism of action of this factor
Distribution of selected trace elements in the major fractions of donkey milk
The aim of this study was to evaluate the concentrations of Zn, Cu, Mn, Se, Mo, Co, Li, B, Ti, Cr, Rb, Sr, Cd, and Pb in donkey milk and their distribution in major milk fractions (i.e., fat, casein, whey proteins, and aqueous phase). Individual milk samples were provided by 16 clinically healthy lactating donkeys. Subsequent centrifugation, ultracentrifugation, and ultrafiltration were carried out to remove fat, casein, and whey proteins to obtain skim milk, a supernatant whey fraction, and the aqueous phase of milk, respectively. Concentrations of the elements were measured in whole milk and fractions by inductively coupled plasma-mass spectrometry, and the concentrations associated with fat, casein, and whey proteins were then calculated. The effect of removal of fat, casein, and whey proteins was determined by repeated-measures ANOVA. The fat fraction of donkey milk carried a small (âŒ4.5% to 13.5%) but significant proportion of Mo, Co, Ti, Cr, and Sr. The casein fraction in donkey milk carried almost all milk Zn, a majority of Cu and Mn, and most of Mo, Ti, and Sr. Relevant proportions, between 20% and 36%, of Se, Co, and Cr were also associated with caseins. The majority of Se, Co, Li, B, Cr, and Rb, and relevant proportions of Mn, Mo, Ti, and Sr were found in soluble form (ultracentrifuged samples) and distributed between whey proteins and the aqueous phase of milk (ultrafiltered samples). Whey proteins in donkey milk carried the majority of milk Se and Co. All Li and B was present in the aqueous phase of milk, which also contained most Rb and Cr, and 17% to 42% of Mn, Se, Mo, Co, Ti, and Sr
Site-directed mutagenesis and NMR spectroscopic approaches to the elucidation of the structure-function relationships in translation initiation factors IF1 and IF3.
The recent developments in the knowledge of the structure and structure-function relationships of prokaryotic initiation factors IF1 and IF3 obtained in our laboratory by site-directed mutagenesis, biochemical and NMR-spectroscopic approaches are discussed
Solar panels as air Cherenkov detectors for extremely high energy cosmic rays
Increasing interest towards the observation of the highest energy cosmic rays
has motivated the development of new detection techniques. The properties of
the Cherenkov photon pulse emitted in the atmosphere by these very rare
particles indicate low-cost semiconductor detectors as good candidates for
their optical read-out.
The aim of this paper is to evaluate the viability of solar panels for this
purpose. The experimental framework resulting from measurements performed with
suitably-designed solar cells and large conventional photovoltaic areas is
presented.
A discussion on the obtained and achievable sensitivities follows.Comment: 6 pages, 8 eps figures included with epsfig, uses espcrc2.sty. Talk
given at the Sixth Topical Seminar on Neutrino and Astroparticle Physics, San
Miniato, Italy, 17-21 May 199
Sequence-specific recognition of DNA by the C-terminal domain of nucleoid-associated protein H-NS
The molecular determinants necessary and sufficient for recognition of its specific DNA target are contained in the C-terminal domain (H-NSctd) of nucleoid-associated protein H-NS. H-NSctd protects from DNaseI cleavage a few short DNA segments of the H-NS-sensitive hns promoter whose sequences closely match the recently identified H-NS consensus motif (tCG(t/a)T(a/t)AATT) and, alone or fused to the protein oligomerization domain of phage λ CI repressor, inhibits transcription from the hns promoter in vitro and in vivo. The importance of H-NS oligomerization is indicated by the fact that with an extended hns promoter construct (400 bp), which allows protein oligomerization, DNA binding and transcriptional repression are highly and almost equally efficient with native H-NS and H-NSctd::λCI and much less effective with the monomeric H-NSctd. With a shorter (110 bp) construct, which does not sustain extensive protein oligomerization, transcriptional repression is less effective, but native H-NS, H-NSctd::λCI, and monomeric H-NSctd have comparable activity on this construct. The specific H-NS-DNA interaction was investigated by NMR spectroscopy using monomeric H-NSctd and short DNA duplexes encompassing the H-NS target sequence of hns (TCCTTACATT)with the best fit (8 of 10 residues) to the H-NS-binding motif. H-NSctd binds specifically and with high affinity to the chosen duplexes via an overall electropositive surface involving four residues (Thr109, Arg113, Thr114, and Ala116) belonging to the same protein loop and Glu101. The DNA target is recognized by virtue of its sequence and of a TpA step that confers a structural irregularity to the B-DNA duplex
Search for massive rare particles with the SLIM experiment
The search for magnetic monopoles in the cosmic radiation remains one of the
main aims of non-accelerator particle astrophysics. Experiments at high
altitude allow lower mass thresholds with respect to detectors at sea level or
underground. The SLIM experiment is a large array of nuclear track detectors at
the Chacaltaya High Altitude Laboratory (5290 m a.s.l.). The results from the
analysis of 171 m exposed for more than 3.5 y are here reported. The
completion of the analysis of the whole detector will allow to set the lowest
flux upper limit for Magnetic Monopoles in the mass range 10 - 10
GeV. The experiment is also sensitive to SQM nuggets and Q-balls, which are
possible Dark Matter candidates.Comment: Presented at the 29-th ICRC, Pune, India (2005
Search for Intermediate Mass Magnetic Monopoles and Nuclearites with the SLIM experiment
SLIM is a large area experiment (440 m2) installed at the Chacaltaya cosmic
ray laboratory since 2001, and about 100 m2 at Koksil, Himalaya, since 2003. It
is devoted to the search for intermediate mass magnetic monopoles (107-1013
GeV/c2) and nuclearites in the cosmic radiation using stacks of CR39 and
Makrofol nuclear track detectors. In four years of operation it will reach a
sensitivity to a flux of about 10-15 cm-2 s-1 sr-1. We present the results of
the calibration of CR39 and Makrofol and the analysis of a first sample of the
exposed detector.Comment: Presented at the 22nd ICNTS, Barcelona 200
Search for strange quark matter and Q-balls with the SLIM experiment
We report on the search for Strange Quark Matter (SQM) and charged Q-balls
with the SLIM experiment at the Chacaltaya High Altitude Laboratory (5230 m
a.s.l.) from 2001 to 2005. The SLIM experiment was a 427 m array of
Nuclear Track Detectors (NTDs) arranged in modules of cm
area. SLIM NTDs were exposed to the cosmic radiation for 4.22 years after which
they were brought back to the Bologna Laboratory where they were etched and
analyzed. We estimate the properties and energy losses in matter of nuclearites
(large SQM nuggets), strangelets (small charged SQM nuggets) and Q-balls; and
discuss their detection with the SLIM experiment. The flux upper limits in the
CR of such downgoing particles are at the level of /cm/s/sr
(90% CL).Comment: 4 pages, 7 eps figures. Talk given at the 24th International
Conference on Nuclear Tracks in Solids, Bologna, Italy, 1-5 September 200
Bulk Etch Rate Measurements and Calibrations of Plastic Nuclear Track Detectors
New calibrations of CR39 and Makrofol nuclear track detectors have been
obtained using 158 A GeV Pb (82+) and In (49+) ions; a new method for the bulk
etch rate determination, using both cone height and base diameter measurements
was developed. The CR39 charge resolution based on the etch-pit base area
measurement is adequate to identify nuclear fragments in the interval 7 <=
Z/beta <= 49. For CR39 the detection threshold is at REL~50 MeV cm^2/g,
corresponding to a nuclear fragment with Z/beta~7. Base cone area distributions
for Makrofol foils exposed to Pb (82+) ions have shown for the first time all
peaks due to nuclear fragments with Z > 50; the distribution of the etched cone
heights shows well separated individual peaks for Z/beta = 78 - 83 (charge
pickup). The Makrofol detection threshold is at REL 2700 MeV cm^2/g,
corresponding to a nuclear fragment with Z/beta~50.Comment: 11 pages, 5 EPS figures. Submitted to Nucl. Instr. Meth.
The antimicrobial polymer PHMB enters cells and selectively condenses bacterial chromosomes
To combat infection and antimicrobial resistance, it is helpful to elucidate drug mechanism(s) of action. Here we examined how the widely used antimicrobial polyhexamethylene biguanide (PHMB) kills bacteria selectively over host cells. Contrary to the accepted model of microbial membrane disruption by PHMB, we observed cell entry into a range of bacterial species, and treated bacteria displayed cell division arrest and chromosome condensation, suggesting DNA binding as an alternative antimicrobial mechanism. A DNA-level mechanism was confirmed by observations that PHMB formed nanoparticles when mixed with isolated bacterial chromosomal DNA and its effects on growth were suppressed by pairwise combination with the DNA binding ligand Hoechst 33258. PHMB also entered mammalian cells, but was trapped within endosomes and excluded from nuclei. Therefore, PHMB displays differential access to bacterial and mammalian cellular DNA and selectively binds and condenses bacterial chromosomes. Because acquired resistance to PHMB has not been reported, selective chromosome condensation provides an unanticipated paradigm for antimicrobial action that may not succumb to resistance
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