Identification of a mismatch-specific endonuclease in hyperthermophilic Archaea.

The common mismatch repair system processed by MutS and MutL and their homologs was identified in Bacteria and Eukarya. However, no evidence of a functional MutS/L homolog has been reported for archaeal organisms, and it is not known whether the mismatch repair system is conserved in Archaea. Here, we describe an endonuclease that cleaves double-stranded DNA containing a mismatched base pair, from the hyperthermophilic archaeon Pyrococcus furiosus The corresponding gene revealed that the activity originates from PF0012, and we named this enzyme Endonuclease MS (EndoMS) as the mismatch-specific Endonuclease. The sequence similarity suggested that EndoMS is the ortholog of NucS isolated from Pyrococcus abyssi, published previously. Biochemical characterizations of the EndoMS homolog from Thermococcus kodakarensis clearly showed that EndoMS specifically cleaves both strands of double-stranded DNA into 5'-protruding forms, with the mismatched base pair in the central position. EndoMS cleaves G/T, G/G, T/T, T/C and A/G mismatches, with a more preference for G/T, G/G and T/T, but has very little or no effect on C/C, A/C and A/A mismatches. The discovery of this endonuclease suggests the existence of a novel mismatch repair process, initiated by the double-strand break generated by the EndoMS endonuclease, in Archaea and some Bacteria.

Applications of nucleic acid chaperone activity of CspA and its homologues.

In Escherichia coli, the cold shock response is exerted upon temperature change from 37 to 15 degrees C and is characterized by induction of several cold shock proteins including its major cold shock protein, CspA. E. coli CspA family consists of nine members, CspA to CspI. CspA and some of its homologues play a critical role in cold acclimation of cells as RNA chaperones by destabilizing secondary structures in RNAs. Here, we showed that the nucleic acid melting activity of Csp proteins can be used to facilitate reactions, such as RT-PCR or RNA cleavage reactions by endoribonucleases, which are hindered by presence of secondary structures in the DNA/RNA substrate used. The low substrate specificity of Csps together with their compatibility with various enzymes and their stability and activity over a broad temperature range makes them ideal candidates to be used for a variety of processes.

Investigation of the molecular mechanism of ICAN, a novel gene amplification method.

Isothermal and Chimeric primer-initiated Amplification of Nucleic acids (ICAN) allows the amplification of target DNA under isothermal conditions at around 55 degrees C using only a pair of 5'-DNA-RNA-3' chimeric primers, thermostable RNaseH and a DNA polymerase with strand-displacing activity (H. Mukai et al. J. Biochemistry, in the preceding paper in this issue). Here we elucidated the mechanism of ICAN by analysing the nicking site of RNaseH, behaviour of chimeric primers and extension products. We found that the ICAN reaction was composed of two unique mechanisms, multi-priming and template-switching, that were responsible for the highly efficient amplifying capability of ICAN. The simultaneous occurrence of two types of reactions, one based on multi-priming and the other based on template-switching, is likely to drive the DNA amplification in ICAN.

Highly efficient isothermal DNA amplification system using three elements of 5'-DNA-RNA-3' chimeric primers, RNaseH and strand-displacing DNA polymerase.

We developed an efficient method of isothermally amplifying DNA termed ICAN, Isothermal and Chimeric primer-initiated Amplification of Nucleic acids. This method allows the amplification of target DNA under isothermal conditions at around 55 degrees C using only a pair of 5'-DNA-RNA-3' chimeric primers, a thermostable RNaseH and a DNA polymerase with strong strand-displacing activity. ICAN is capable of amplifying DNA at least several times greater than the amount produced with PCR by increasing primer concentration. This method would be applicable for on-site DNA detection including gene diagnosis, and would also be suitable for 'real time' detection when combined with a cycling probe.

Rapid detection and differentiation of the major mycoplasma contaminants in cell cultures using real-time PCR with SYBR Green I and melting curve analysis.

A quantitative real-time polymerase chain reaction (PCR) procedure followed by melting curve analysis, using the green fluorescence dye SYBR Green I, was developed for rapid detection and differentiation of mycoplasma contaminants in cell cultures. This method showed that the detection of the target sequence was linear over a range from 10(4) to 10 colony-forming units (CFU) of the mycoplasma cells. Analysis of the melting temperature of the PCR products allowed differentiation of the major mycoplasma contaminants. These results demonstrate that the protocol described in the present study can decrease the time to obtain reproducible results by simultaneous detection and differentiation of the Mycoplasma species contaminating cell cultures.