Cloning and characterization of the MboU restriction- modification system

The two genes encoding the class IIS restriction-modification system Afboll from Moraxella bovls were cloned separately in two compatible plasmids and expressed in E. coll RR1AM15. The nucleotide sequences of the Afboll endonuclease (R.Afboll) and methylase (M.Afboll) genes were determined and the putative start codon of R.Afboll was confirmed by amino acid sequence analysis. The mbollR gene specifies a protein of 416 amino acids (MW: 48,617) while the mbollM gene codes for a putative 260-residue polypeptide (MW: 30,077). Both genes are aligned in the same orientation. The coding region of the methylase gene ends 11 bp upstream of the start codon of the restrictase gene. Comparing the amino acid sequence of M.Afboll with sequences of other N6-adenine methyltransferases reveals a significant homology to M.Rsri, M.HInfl and M.DpnA. Furthermore, M.Afboll shows homology to the N4-cytosine methyltransferase BamH\