Yunhao Liu

Determining the mechanism of action of HutD - a regulatory governor of gene expression.

The histidine utilization locus (hut) confers Pseudomonas fluorescens SBW25 with an ability to grow on histidine as a sole carbon and/or nitrogen source. Regulation of hut is complex and not fully understood. Previous work (Zhang & Rainey, 2007) showed that HutD (a protein to which no previous function had been assigned) functions as a governor of hut expression that sets an upper limit to the level of hut activity. Zhang & Rainey (2007) argued that the need for such a governor made sense in light of the positive feed forward regulation involving repressor HutC and the potentially harmful effects of metabolising histidine at too high a rate (degradation of histidine liberates ammonia, in fact two molecules of ammonia are liberated per molecule of histidine).

The mechanism of HutD action is unknown, although several hypotheses exist. One of these is that HutD acts as a molecular sponge and controls the intracellular concentration of urocanate (urocanate is the first break-down product of histidine and the specific inducer of hut). My work concerns the purifcation and characterization of HutD in order to test this hypothesis (and several others). This work is a collaboration with Vic Arcus and was recently supported by a grant from The Maurice and Phyllis Paykel Trust.