| Summary: | Previous work by Henderson (1996), identified a sub-genic fragment (473 bp) with a partial open reading frame (ORF) homologous to htrA, but mutation of the C. jejuni gene failed to identify a phenotype. The ORF was mapped to a 2.38kb Bg/II fragment but only the downstream portion which included 3' htrA sequence could be cloned. The 5' end of a RR was identified downstream of htrA and showed similarity to members of the OmpR sub-family, including cpxR from E. coli. The objective of the work described in this thesis was to characterise the 5' region of htrA, to determine the level of expression and establish if this expression is regulated by the downstream TCR. This study focused on both the htrA gene and the presence of a putative two-component regulatory system downstream because of the possible involvement of the TCR system in regulator htrA in C. jejuni. Genetic analysis revealed 5' sequence data of htrA including the promoter region and the sequence confirmed the protein as a member of the family of htrA heat shock proteases. Analysis of the promoter region failed to indicate the type of regulation which the gene is under but it was established that htrA gene is expressed under normal growth conditions, but not in response to temperature. A two-component system designated, regX4/regY4 (RR/HPK), was identified downstream of htrA and shares basic amino acid sequence features with the orthodox E. coli ompR/envZ system. Characterisation of the putative regX4/regY4 system by mutational analysis was difficult as all efforts to create a regx4 mutant were unsuccessful although a regY4 mutant was readily obtained allowing preliminary phenotypic analysis to be performed. It remains to be established whether the putative regX4/regY4 TCR system regulates htrA expression in C. jejuni although the mechanisms are in now in place whereby any possible regulatory relationship can be investigated.
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