Cloning and expression of the BalI restriction-modification system

BalI, a type II restriction-modification (R-M) system from the bacterium, Brevibacterium albidum, recognized the DNA sequence 5'-TGGCCA-3'. We cloned the genes encoding the BalI restriction endonuclease and methyltransferase and expressed them in Escherichia coli. The two genes were aligned tail-to-tail and their termination codons overlapped. BalI 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 to that of other m⁶A MTases, although it has been categorized as m⁵C methyltransferase. A high expression system for the BalI restriction endonuclease was constructed in E.coli for the production of large quantities of enzyme.