Identification of the CTAG-recognizing restriction-modification systems MthZI and mthFI from Methanobacterium thermoformicicum and characterization of the plasmid-encoded mthZIM gene

Abstract

Two CTAG-recognlzing restriction and modification (R/M) systems, designated MthZI and MthFI, were identified in the thermophllic archaeon Methanobacterium thermoformicicum strains Z-245 and FTF, respectively. Further analysis revealed that the methyltransferase (MTase) genes are plasmid-located in both strains. The plasmid pFZ1-encoded mthZIM gene of strain Z-245 was further characterized by subclonlng and expression studies in Escherlchla coli followed by nucleotide sequence analysis. The mthZIM gene Is 1065 bp in size and may code for a protein of 355 amlno acids (Mr 42,476 Da). The deduced amino acid sequence of the M.MthZI enzyme shares substantial similarity with four distinct regions from several m4C-and m6A-MTases, and contains the TSPPY motif that is so far only found in m4C-MTases. Partially overlapping with the mthZIM gene and in reverse orientation, an additional ORF was identified with a size of 606 bp potentially coding for a protein of 202 amino acids (Mr 23.710 Da). This ORF is suggested to encode the corresponding endonuclease R.MthZI. © 1992 Oxford University Press.