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The Stoffel DNA fragment, shortened by 12 bp from 5' end, coding for StoffelDNA polymerase (missing 4 amino acids at N-terminus of Stoffel amino-acids sequence) from the thermophilic Thermus aquaticus (strain YT-1) was amplified, cloned and expressed in Escherichia coli. The recombinant Stoffel fragment contained a polyhistidine tag at the N-terminus (21 additional amino acids) that allowed its single-step isolation by Ni2+ affinity chromatography. The enzyme was characterized and displayed high DNA polymerase activity and thermostability evidently higher than the native Tag DNA polymerase.
We describe a fast and very efficient method of purification which yields highly purified integration host factor-like proteins in one chromatografie step. IHF-like proteins from Acinetobacter junii or Proteus vulgaris are each an a£ heterodimer (subunits of 10 and 11 kDa) similar to the IHF of Escherichia coli when analyzed by polyacrylamide gel electrophoresis. The purified IHF are able to bind to the same ihf sites as IHF of E. coli. The results presented confirm that IHF is conserved during evolution in gram-negative bacteria.
The Tth DNA polymerase gene from the thermophilic Thermus thermophilus (strain HB8) was amplified, cloned and expressed in Escherichia coli. The recombinant DNA polymerase containing a polyhistidine tag at the N-terminus was isolated in a single step by Ni2+ affinity chromatography. The purified recombinant enzyme, showing high polymerase activity contained 43 additional amino-acid residues (including a cluster of six histidine residues inserted for purification of the recombinant protein by metal-affinity chromatography) at N-terminus. The applied overexpression system was very efficient giving 700000 u of DNA polymerase activity from 1 liter of induced culture. The enzyme was characterized and displayed high DNA polymerase and reverse transcriptase activities and high thermostability as compared to the native Tht DNA polymerase.
The integration host factor (IHF) is a sequence-specific, histone-like, multi-fun- ctional DNA-binding and -bending protein of Escherichia coli. Characterization and functional analysis of this protein has been carried out mainly in bacteriophage λ and other mobile genetic elements. In this paper we report data concerning the binding of IHF protein to the plasmid oripl5A region. IHF binds to the single site of the DNA fragment containing the oripl5A, as shown by the gel mobility shift assays and footprinting experiment. On the basis of the ihf consensus sequences published, we have been able to identify one sequence of putative ihf site into the oripl5A sequence with two mismatches in relation to the consensus sequence of Kur et al., 1989, Gene 81,1-15. One ihf binding site was also found in the oriColEl region sequence with three mismatches in relation to this consensus sequence.
To study the biochemical properties of SSB's from Deinococcus grandis (DgrSSB) and Deinococcus proteolyticus (DprSSB), we have cloned the ssb genes obtained by PCR and have developed Escherichia coli overexpression systems. The genes consist of an open reading frame of 891 (DgrSSB) and 876 (DprSSB) nucleotides encoding proteins of 296 and 291 amino acids with a calculated molecular mass of 32.29 and 31.33 kDa, respectively. The amino-acid sequence of DgrSSB exhibits 45%, 44% and 82% identity and the amino-acid sequence of DprSSB reveals 43%, 43% and 69% identity with Thermus aquaticus (TaqSSB), Thermus thermophilus (TthSSB) and Deinococcus radiodurans SSBs, respectively. We show that DgrSSB and DprSSB are similar to Thermus/Deinococcus SSBs in their biochemical properties. They are functional as homodimers, with each monomer encoding two single-stranded DNA binding domains (OB-folds). In fluorescence titrations with poly(dT), both proteins bind single-stranded DNA with a binding site size of about 33 nt per homodimer. In a complementation assay in E. coli, DgrSSB and DprSSB took over the in vivo function of EcoSSB. Thermostability with half-lives of about 1 min at 65-67.5°C make DgrSSB and DprSSB similar to the known SSB of Deinococcus radiodurans (DraSSB).
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