The mannitol operon of Escherichia coli, encoding the mannitol-specific enzyme II of the phosphotransferase system (MtlA) and mannitol phosphate dehydrogenase (MtlD) contains an additional downstream open reading frame which encodes the mannitol repressor (MtlR).
Jiyao W et al.(2023). "The conserved domain database in 2023.",