Abstract
A DNA methyltransferase, M.PabI, of a hyperthermophilic archaeon Pyrococcus abyssi was purified and characterized. Some restriction-modification genes behave as “selfish” mobile genetic elements, just as transposons, and they are often found associated with genomic rearrangements or polymorphisms. This nature helped us to identify a putative restriction-modification gene pair on P. abyssi genome through its comparative analysis with that of another Pyrococcal species. Its constituent restriction enzyme was identified by our previous work as a hyper-thermoresistant DNA endonuclease, PabI, which catalyzes cleavage at 5'-GTA/C-3'. In this study, M.PabI, the DNA methyltransferase of PabI restriction-modification system, was over-expressed in Escherichia coli and purified. We describe detailed enzymatic characterization of this enzyme, which includes measurements of thermodynamic and kinetic parameters. It generates 5'-GTm6AC-3' and is inhibited by Zn2+. It turned out to be the most thermophilic of all the reported DNA methyltransferases.
