A P subtype restriction enzyme that recognizes the double-stranded sequence 5'-CTCGAG-3'; the cleavage site is unknown. Endonucleolytic cleavage of DNA to give specific double-stranded fragments with terminal 5'-phosphates. BsuMI restriction activity requires YdiR, YdiS and YdjA. Not expressed during sporulation. Constitutively expressed during exponential growth. Encoded in an operon with ydiS and ydjA. Not essential; its disruption results in increased transformation by plasmid DNA carrying multiple BsuMI target sequences (PubMed:11751814). Triple deletion ydiO-ydiP-ydiS leads to loss of susceptibility to MspJI, which only digests C-methylated DNA (PubMed:32324221).