Investigating the molecular basis for autorepression of a gene promoter from the α-proteobacterium Sinorhizobium meliloti

Abstract

Autorepression is an intrinsic pathway of autoregulation developed to maintain homeostasis in biological systems. The srlA gene encodes a predicted thioredoxin-like protein and deletion of srlA results in increased sensitivity to salt and oxidizing agents in the nitrogen-fixing facultative endosymbiont, Sinorhizobium meliloti. The srlA promoter is autorepressed by an unknown mechanism. In my thesis, I investigate the mechanism of the autorepression phenotype. Chapter 1 is a literature review and provides an overview of the srlA promoter and gene, the autorepression phenotype observed, as well as possible autorepression mechanisms. Chapter 2 documents a bioinformatic analysis of SrlA protein structure and possible subcellular location, and an experimental analysis of whether the thioredoxin-like C-X-X-C motif of SrlA is required for the autorepression phenotype. Chapter 3 details the use of transposon mutagenesis and a promoter activation screen to investigate the possibility that other S. meliloti genes play a role in the autorepression of srlA. Chapter 4 investigates whether gene srlA is required for effective nodulation and growth stimulation of the S. meliloti plant host, alfalfa (Medicago sativa). Finally, Chapter 5 includes a summary of the thesis and concluding statements.