HutD from Pseudomonas fluorescens SBW25 is a component of the histidine uptake and utilisation operon. HutD is operonic with the well characterised repressor protein HutC. Genetic analysis using transcriptional fusions (lacZ) and deletion mutants shows that hutD is necessary to maintain fitness in environments replete with histidine. Evidence outlined by Zhang & Rainey (2007) suggests that HutD functions as a governor that sets an upper bound on the level of hut operon transcription [1]. The mechanistic basis is unknown, but in silico molecular docking studies based on the crystal structure of PA5104 (HutD from Pseudomonas aeruginosa) show that urocanate (the first breakdown product of histidine) docks with the active site of HutD.

1: Genetic analysis of the histidine utilization (hut) genes in Pseudomonas fluorescens SBW25. Zhang XX, Rainey PB; Genetics. 2007;176:2165-2176. PMID:17717196