Involved in the repression of the expression of the mannitol mtlADR operon. Does not bind the operator/promoter regulatory region of this operon. Therefore, seems to belong to a new class of transcription factors in bacteria that may regulate gene expression indirectly, perhaps as a part of a larger transcriptional complex. Homodimer. Can also form higher level multimer aggregates. Belongs to the MtlR/FumE family.