Nucleotide sequence of the gene encoding the BstLVI DNA methyltransferase: comparison with other amino-DNA methyltransferases.

The nucleotide sequence of a 2837-base pairs (bp) EcoRI-PvuI fragment of Bacillus stearothermophilus LV chromosomal DNA encoding the bstLVIM gene was determined. It revealed a large open reading frame (ORF) of 1737 bp specifying a methylase of 579 amino acid (aa) residues and Mr 66,831. This was in agreement with the size estimated for the M. BstLVI ( approximately 67 kDa) purified from Escherichia coli cells harboring a recombinant plasmid containing the bstLVIM gene and with results of transcription-translation experiments performed in vitro. Upstream the bstLVIM gene and in the opposite transcriptional orientation, there is a 81-aa ORF that showed great homology with the regulatory C proteins identified in other type II restriction and modification (R-M) systems. This 81-aa ORF precedes a truncated ORF of 86 aa which in turn may represent the structural gene for the BstLVI restriction endonuclease.