Cloning and nucleotide sequence of the genes coding for theSau961 restriction and modification enzymes

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Abstract
The genes coding for the GGNCC specific Sau961 restriction and modification enzymes were cloned and expressed in Escherichia coli. The DNA sequence predicts a 430 amino acid protein (Mr: 49,252) for the methyltransferase and a 261 amino acid protein (Mr: 30,486) for the endonuclease. No protein sequence similarity was detected between the Sau961 methyltransferase and endonuclease. The methyltransferase contains the sequence elements characteristic for m5C-methyltransferases. In addition to this, M.Sau961 shows similarity, also in the variable region, with one m5C-methyltransferase (M.SinI) which has closely related recogition specificity (GFA/TCC). M.Sau961 methylates the internal cytosine within the GGNCC recognition sequence. The Sau961 endonuclease appears to act as a monomer.