Cloning and regulation of gene expression of EcoRV restriction- modification system

A number of recombinant plasmids, containing EcoRV restriction-modification genes have been constructed. Individual genes of this system were introduced into plasmids of various incompatibility groups. Promoter regions of genes encoding methylase and restrictase have been cloned and studied. With the use of specialized vector pVE8 it was shown that the efficiency of the endonuclease gene promoter is comparable with early lambda phage promoters and produced about 70% of PL efficiency. The efficiency of the methylase gene promoter region was twice less than the efficiency of the restriction endonuclease gene promoter. Plasmid with restriction endonuclease gene promoter located downstream in relation to the additional regulatable phage lambda promoter PL has been obtained. It enabled us to construct strains 30-40 fold overproducing this enzyme under conditions of inactivation of the temperature sensitive phage repressor c1857. This construction directs the production of a high level (10%) of the total cellular soluble proteins) of the EcoRV restriction enzyme. The factors that influenced the level of enzyme synthesis under induction are discussed.     

Enzymic in vitro repair and chemical nature of DNA chain breaks induced by incorporated phosphorus-32P decay.

In vitro repair of single strand breaks in T4 and phage DNA caused by 32p decay was studied. Zone centrifugation procedure showed that polynucleotide kinase, ligase enzyme system failed to repair 32P-damages. It was found that damaged DNA contained gaps and could be repaired by DNA-polymerase I, polynucleotide ligase treatment.     

C-Terminal Domain of Bacillus cereus Hemolysin II Is Able to Interact with Erythrocytes

Russian Journal of Bioorganic Chemistry - Hemolysin II (HlyII) is one of the pathogenic factors of Bacillus cereus. With respect to the prototype of β-barrel toxins, the α-toxin of S....     

The Pore-Forming Properties of SsoHel308 Helicase from Saccharolobus solfataricus

The pore-forming activity of SsoHel308 helicase from extreme thermophilic archaea Saccharolobus solfataricus has been demonstrated for the first time. This protein embedded in rabbit erythrocyte membranes may cause erythrocyte hemolysis. It has been shown that this enzyme forms pores in a planar artificial bilayer membrane and acts as a transformer. After embedding this enzyme into biolayer lipid membranes, the membrane conductivity is altered. Taken together, our results show that SsoHel308 helicase is able to form pores in artificial bilayer membranes and, in some cases, the current that flows across the membranes shares features typical of ion channels. The short lifetime of the pores in the membrane significantly reduces the toxicity of helicase for a living cell. The possibility of directed translocation of single-stranded DNA in the presence of ATP will enable the use of this enzyme as a molecular syringe for injecting single-stranded DNA into living cells.

     

Characterization of pECL18 and pKPN2: a proposed pathway for the evolution of two plasmids that carry identical genes for a Type II restriction-modification system

The primary structures of the plasmids pECL18 (5571 bp) and pKPN2 (4196 bp) from Escherichia coli and Klebsiella pneumoniae, respectively, which carry genes for a Type II restriction-modification system (RMS2) with the specificity 5'-CCNGG-3', were determined in order to elucidate the structural relationship between them. The data suggest a possible role for recombination events at bom (basis of mobility) regions and the sites of resolution of multimer plasmid forms (so-called cer sequences) in the structural evolution of multicopy plasmids. Analysis of the sequences of pECL18 and pKPN2 showed that the genes for RM* Ecl18kI and RM* Kpn2kI, and the sequences of the rep (replication) regions in the two plasmids, are almost identical. In both plasmids, these regions are localized between the bom regions and the cer sites. The rest of the pECL18 sequence is almost identical to that of the mob (mobilization) region of ColE1, and the corresponding segment of pKPN2 is almost identical to part of pHS-2 from Shigella flexneri. The difference in primary structures results in different mobilization properties of pECL18 and pKPN2. The complete sequences of pECL18, pKPN2 and the pairwise comparison of the sequences of pECL18, pKPN2, ColE1 and pHS-2 suggest that plasmids may exchange DNA units via site-specific recombination events at bom and cer sites. In the course of BLASTN database searches using the cer sites of pECL18 and pKPN2 as queries, we found twenty cer sites of natural plasmids. Alignment of these sequences reveals that they fall into two classes. The plasmids in each group possess related segments between their cer and bom sites.     

Construction of an overproducing strain,purification, and biochemical characterization of the 6His-Eco29kI restriction endonuclease

We constructed a strain of Escherichia coli overproducing 6His-tagged Eco29kI by placing the coding sequence under control of a strong bacteriophage T5 promoter. The yield of 6His-Eco29kI restriction endonuclease expression could be increased to about 20% of the total cellular protein, but inclusion bodies formed consisting of insoluble 6His-Eco29kI protein. We developed a fast and effective protocol for purification of the homogeneous enzyme from both soluble and insoluble fractions and established their identity by catalytic activity assay. The isolated enzymes were tested for recognition specificity and optimal reaction conditions as a function of NaCl and KCl concentrations, temperature, and pH compared with the native Eco29kI restriction endonuclease. The 6His-tagged enzyme retained the specificity of the native protein but had an altered optimum of its catalytic reaction.     

Restriction endonucleases from various bacterial strains exhibit an ice-nucleating activity

Six strains containing site-specific endonucleases II were selected from a collection of 45 ice-nucleating bacterial strains isolated from rhizosphere of plants growing in various geographical regions. Endonucleases Pfl211I, Psp8I, and Psp23I were isolated and purified from two Pseudomonas sp. strains and a Pseudomonas fluorescens strain. Restriction endonucleases Pfl21I and Psp23I were shown to recognize and cleave the DNA nucleotide sequence 5'-CTGCA decrease G-3'. Endonuclease Psp8I recognized and cleaved the DNA nucleotide sequence 5'-G decrease GATCC-3'. These endonucleases were found to be true isoschizomers of PstI and BamHI, respectively.