The E. coli Anti-Sigma Factor Rsd: Studies on the Specificity and Regulation of Its Expression

Background: Among the seven different sigma factors in E. coli s 70 has the highest concentration and affinity for the core RNA polymerase. The E. coli protein Rsd is regarded as an anti-sigma factor, inhibiting s 70-dependent transcription at the onset of stationary growth. Although binding of Rsd to s 70 has been shown and numerous structural studies on Rsd have been performed the detailed mechanism of action is still unknown. Methodology/Principal Findings: We have performed studies to unravel the function and regulation of Rsd expression in vitro and in vivo. Cross-linking and affinity binding revealed that Rsd is able to interact with s 70, with the core enzyme of RNA polymerase and is able to form dimers in solution. Unexpectedly, we find that Rsd does also interact with s 38, the stationary phase-specific sigma factor. This interaction was further corroborated by gel retardation and footprinting studies with different promoter fragments and s 38-ors 70-containing RNA polymerase in presence of Rsd. Under competitive in vitro transcription conditions, in presence of both sigma factors, a selective inhibition of s 70-dependent transcription was prevailing, however. Analysis of rsd expression revealed that the nucleoid-associated proteins H-NS and FIS, StpA and LRP bind to the regulatory region of the rsd promoters. Furthermore, the major promoter P2 was shown to be down-regulated in vivo by RpoS, the stationary phase-specific sigma factor and the transcription factor DksA, while induction of the stringent control enhanced rsd promoter activity. Most notably, the dam-dependent methylation of a cluster of GATC sites turned ou

Evidence for octupole vibration in the triaxial superdeformed well of Lu164

High-spin states in Lu164 were populated in the Sb121(Ca48,5n) reaction at 215 MeV and γ-ray coincidences were measured with the Gammasphere spectrometer. Through this experiment the eight known triaxial superdeformed bands in Lu164 could be confirmed. Some of these bands were extended to higher as well as to lower spins. Evidence is reported for the first time for weak ΔI=1,E1 transitions linking TSD3 and TSD1. This observation may imply coupling to octupole vibrational degrees of freedom. The decay mechanism is different from the one observed in the neighboring even-N isotopes, which exhibit wobbling excitations built on the πi13/2 structure with E2(M1),ΔI=1 interband decay. An additional sequence decaying at high spin into TSD1 was observed up to Iπ=(50-). This band has a constant dynamic moment of inertia of ∼70 2MeV-1 and an alignment that is ∼2 larger than that found for TSD1. A revision of the assumed spin-parity-assignment of TSD2 is based on the observed decay-out to normal-deformed structures. The parity and signature quantum numbers of TSD2 are now firmly assigned as (π,α)=(+,0), in disagreement with the former assignment of (π,α)=(-,1), which was based on the assumption that TSD2 is the signature partner of TSD1. TSD1 and TSD2 show an alignment gain at ω∼0.67 and 0.60 MeV, respectively. In TSD1 the involvement of the j15/2 neutron orbital is suggested to be responsible for the high-frequency crossing

Collective and noncollective excitations in 122Te

High-spin states in 122Te were populated in the reaction 82Se(48Ca, α4n)122Te at a beam energy of 200 MeV and γ-ray coincidences were measured with the Gammasphere spectrometer. The previously known level scheme was extended to considerably higher spin. Maximally aligned states and several high-energy transitions feeding into some of these levels were observed. In addition, seven collective high-spin bands were discovered for the first time in this nucleus. The experimental results are compared with cranked Nilsson-Strutinsky model calculations and possible configuration assignments to the new high-spin structures are discussed

High-spin spectroscopy in Xe125

Levels excited up to 39.8 MeV and 119/2 units of angular momentum have been populated in Xe125 by the 82Se(Ca48,5n)Xe125 reaction. High-fold γ-ray coincidence events were measured using the Gammasphere Ge detector array. Nine regular rotational bands extending from levels identified previously up to almost 60ℏ have been identified, and three of these have been connected to low-lying levels having well-established spins and parities. Configurations have been assigned to six of the bands based on alignment properties, band crossings, and comparison with theoretical cranked shell model calculations (CSM). Transition quadrupole moments have been measured for these bands in the spin range 31-55ℏ and were found to be in agreement with the CSM calculations. The corresponding quadrupole deformation ε2 ranges from 0.28 to 0.34 at a γ deformation of 0° and from 0.29 to 0.36 at a γ value of 5°

Noncollective aligned and antialigned states in I125

High-spin states in I125 were populated using the reaction Se82(Ca48,p4n) at a beam energy of 200 MeV and γ-ray coincidence events were acquired with the Gammasphere spectrometer. The level scheme of I125 was extended considerably. In particular, maximally aligned states involving all eleven particles outside the Sn114 core were observed. Comparison with cranked Nilsson-Strutinsky calculations suggests that three of these states are the final Imax states in terminating bands with all spin vectors aligned along a common axis. In two of these, one spin vector is antialigned and points in the opposite direction. In one of the states two spin vectors are antialigned. This is the first observation of a state with such a structure

Highly deformed high-spin band in 125I

High-spin states in 125I have been investigated using the reaction 82Se(48Ca,p4n) at a beam energy of 200 MeV and γ-ray coincidence events were detected using the Gammasphere spectrometer. A deformed rotational band, extending up to Iπ=95/2-, was observed for the first time in a heavier odd-A iodine nucleus. The characteristics of the band are very similar to those of the highly deformed bands observed recently in neighboring nuclei and it is essentially identical to one of the previously known bands in 126Xe. The experimental results are compared to cranked Nilsson-Strutinsky calculations and possible configurations for the band are discussed

Indication for hyperdeformed cluster states in

An activation technique was used to investigate relative yields of fission products from the reaction 232Th(n, f ) for neutron energies between 1.3 and 1.8MeV covering the region around the first hyperdeformed resonances. Intensities of characteristic γ-ray transitions were analyzed to search for changes in the mass distribution for neutron energies corresponding to the resonances and below the resonances. Relative increases in yield between 7 and 23% are observed for A ≈ 100 and 132 in the resonance region around 1.6MeV. It is proposed that the yield enhancement of daughter nuclei of the preformed fragments 132Sn and 101Zr arises from cold fission of a di-cluster configuration. The experimental results support theoretical predictions for the existence of hyperdeformed octupole shapes based on the di-nuclear configuration 132Sn + 101Zr

First triaxial superdeformed band in \chem{^{170}Hf}

First evidence is presented for triaxial superdeformation in $^{170}$Hf. High-spin states in this nucleus have been investigated in a $\gamma$-ray coincidence measurement using the EUROBALL spectrometer array. A new band was discovered which has moments of inertia that are very similar to the ones of triaxial superdeformed bands in neighbouring Hf and Lu nuclei. The intensities with which these bands are populated are different from what may be expected from calculated potential-energy minima

First evidence for triaxial superdeformation in \chem{^{161}Lu} and \chem{^{162}Lu}

High-spin states in $^{161}$Lu and $^{162}$Lu have been investigated using the GASP $\gamma$-ray spectrometer array. Excited states in these nuclei have been populated through the $^{100}$Mo($^{65}$Cu, $x$n) reaction at a beam energy of 260 MeV. Four presumably triaxial superdeformed bands, three in $^{162}$Lu and one in $^{161}$Lu, have been observed. This is the first evidence for triaxial superdeformation in the two isotopes