The sialic acid catabolic and transport operons and pathway. A. Schematic diagram of the nan and siaPT operons. The nan operon encodes for the entire catabolic pathway and the transcriptional regulator SiaR. The siaPT operon encodes for the sialic acid transporter and YjhT, a sialic acid mutarotase. The accession numbers for the KW-20 Rd sequence are indicated below each gene. B. The sialic acid catabolic pathway.