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The major chaperone genes of Helicobacter pylori are negatively regulated by HspR, a homologue of the repressor of the dnaK operon of Streptomyces coelicolor. Using an in vitro selection and amplification approach we identified two new chromosomal binding sites of the HspR protein. Both binding sites were characterized by footprinting analysis with purified HspR protein. Intriguingly, these HspR binding sites are located at the 3prime prime or minute ends of two genes coding for predicted proteins with functions unrelated to those of chaperones. This suggests that H. pylori HspR may regulate the expression of genes encoding proteins with diverse functions. Nucleotide sequence alignment of HspR-binding sites highlights conserved nucleotides extending outside the previously proposed consensus binding sequence with structural features predicting geometry of HspR binding as an oligomer. 相似文献
115.
A genomic library of the hyperthermophilic archaeon Sulfolobus solfataricus strain MT4 was constructed in Escherichia coli using a cloning vector not designed for heterologous gene expression. One positive clone exhibiting acquired thermophilic acetylesterase activity was directly detected by an in situ plate assay using a colony staining procedure with the chromogenic substrate beta-naphthyl acetate. The plasmid isolated from the clone contained a 3.3 kb genomic fragment from S. solfataricus and a full-length esterase coding sequence could be identified. Expression of the active thermostable esterase in E. coli was independent of isopropyl-beta-D-thiogalactopyranoside and of the kind of vector, suggesting that the archaeal esterase gene was controlled by fortuitous bacterial-like sequences present in its own 5' flanking region, not by the bacterial lac promoter or other serendipitous vector-located sequences. The protein, partially purified by thermoprecipitation of the host proteins at high temperature and gel exclusion chromatography, showed a homo-tetrameric structure with a subunit of molecular mass of 32 kDa which was in perfect agreement with that deduced from the cloned gene. The same protein was revealed in S. solfataricus cell extracts, thus demonstrating its functional occurrence in vivo under the cell culture conditions tested. The recombinant enzyme exhibited high thermal activity and thermostability with optimal activity between pH 6.5 and 7.0. The hydrolysis of p-nitrophenyl esters of fatty acids (from C(2) to C(8)) allowed the enzyme to be classified as a short length acyl esterase. 相似文献
116.
Bongiorno D Ceraulo L Mele A Panzeri W Selva A Turco Liveri V 《Carbohydrate research》2002,337(8):743-754
The stoichiometry, geometry, stability, and solubility of the inclusion complexes of melatonin (MLT) with native cyclomaltooligosaccharides (alpha-, beta- or gamma-cyclodextrins, CDs) are determined experimentally by high-resolution NMR spectroscopy, calorimetric and solubility measurements, and mass spectrometry. The observed differences are discussed in terms of molecular recognition expression of the host-guest (h-g) interactions within the hydrophobic CDs cavities of different size. The 1:1 h-g stoichiometry in water solution prevails at low CD concentrations; the trend to form higher order associations is observed at increasing CD concentrations. The stability order beta-CD>gamma-CD>alpha-CD for the complexes in water solution and beta-CD>alpha-CD>gamma-CD for the protonated or alkali-cationated complexes in the gas phase are rationalized on the grounds of the structural data from NMR spectroscopy and of the thermodynamic parameters from calorimetric measurements. 相似文献
117.
The interactions between biocontrol fungi and bacteria may play a key role in the natural process of biocontrol, although
the molecular mechanisms involved are still largely unknown. Synergism can occur when different agents are applied together,
and cell wall degrading enzymes (CWDEs) produced by fungi can increase the efficacy of bacteria. Pseudomonas spp. produce membrane-disrupting lipodepsipeptides (LDPs) syringotoxins (SP) and syringomycins (SR). SR are considered responsible
for the antimicrobial activity, and SP for the phytotoxicity. CWDEs of Trichoderma spp. synergistically increased the toxicity of SP25-A or SRE purified from P. syringae against fungal pathogens. For instance, the fungal enzymes made Botrytis cinerea and other phytopathogenic fungi, normally resistant to SP25-A alone, more susceptible to this antibiotic. Pseudomonas produced CWDEs in culture conditions that allow the synthesis of the LDPs. Purified bacterial enzymes and metabolites were
also synergistic against fungal pathogens, although this mixture was less powerful than the combination with the Trichoderma CWDEs. The positive interaction between LDPs and CWDEs may be part of the biocontrol mechanism in some Pseudomonas strains, and co-induction of different antifungal compounds in both biocontrol bacteria and fungi may occur.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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Ayora S Piruat JI Luna R Reiss B Russo VE Aguilera A Alonso JC 《Journal of molecular biology》2002,316(1):35-49
The moss Physcomitrella patens, which is a land plant with efficient homologous recombination, encodes two Rad51 proteins (PpaRad51.1 and PpaRad51.2). The PpaRad51.1 and PpaRad51.2 proteins, which share 94 % identity between them, interact with themselves and with each other. Both proteins bind ssDNA and dsDNA in a Mg(2+) and pH-dependent manner, with a stoichiometry of one PpaRad51.1 monomer per 3(+/-1) nt or bp and one PpaRad51.2 monomer per 1(+/-0.5) nt or bp, respectively. At neutral pH, a 1.6-fold excess of both proteins is required for ssDNA and dsDNA binding. PpaRad51.1 and PpaRad51.2 show ssDNA-dependent ATPase activity and efficiently promote strand annealing in a nucleotide-independent but in a Mg(2+)-dependent manner. Both proteins promote joint-molecule formation, DNA strand invasion and are able to catalyse strand exchange in the presence of Mg(2+) and ATP. No further increase in the activities is observed when both proteins are present in the same reaction. None of the PpaRad51 gene products complement the DNA repair and recombination phenotype of Saccharomyces cerevisiae rad51delta mutants. However, PpaRad51.1 confers a dominant-negative DNA repair phenotype, and both PpaRad51 proteins reduce the levels of double-strand break-induced recombination when overexpressed in S. cerevisiae wt cells. These results suggest that both PpaRad51 proteins are bona fide Rad51 proteins that may contribute, in a different manner, to homologous recombination, and that they might replace ScRad51 in a hypothetical yeast protein complex inactivating different functions required for recombinational repair. 相似文献
120.
Tanno B Negroni A Vitali R Pirozzoli MC Cesi V Mancini C Calabretta B Raschellà G 《The Journal of biological chemistry》2002,277(26):23172-23180