Negatively regulates the expression of the ganSPQAB operon (PubMed:2104611, PubMed:9287030, PubMed:27501980). Inhibits transcription of the operon by binding to an operator in the promoter region (PubMed:27501980). In the presence of galactobiose, GanR dissociates from the promoter, resulting in the expression of the gan operon (PubMed:27501980).