CLONING AND EXPRESSION OF THE BALI RESTRICTION-MODIFICATION SYSTEM

BalI, a type II restriction-modification (R-RA) system from the bacter ium, Brevibacterium albidum, recognizes the DNA sequence 5'-TGGCCA-3', We cloned the genes encoding the BalI restriction endonuclease and me thyltransferase and expressed them in Escherichia coli. The two genes were aligned tail-to-tail and their termination codons overlapped, Bal I restriction endonuclease and methyltransferase comprise 260 and 280 amino acids, respectively and have molecular weights of 29 043 and 31 999 Da, The amino acid sequence of BalI methyltransferase is similar t o that of other m(6)A MTases, although it has been categorized as a m( 5)C methyltransferase, A high expression system for the BalI restricti on endonuclease was constructed in E. coli for the production of large quantities of enzyme.