A comparative analysis of transcriptional attenuation in theilvGMEDA operon of Enterobacteriaceae

Jennie Lee Williams, Purdue University

Abstract

The sequence similarity within the ilvGMEDA leader transcript of a number of enteric organisms (i.e., Escherichia coli, Edwardsiella tarda, and Serratia marcescens) is striking; however, regions upstream of the transcriptional start sites exhibit more differences from each other. The E. coli ilvGMEDA leader generates, in vitro, two transcripts originating from two promoters (P$\sb1$ and P$\sb2)$. In vivo, however, only P$\sb2$ functions. In contrast, while analyzing the ilvGMEDA leader of E. tarda and S. marcescens, it was found that only one transcript corresponding to the P$\sb2$ transcript of the E. coli ilv leader is formed in vitro. In this study the promoter regions of E. coli, E. tarda, and S. marcescens have been analyzed and compared both in vitro and in vivo. We have seen that the nusA gene product prolongs the length of the pause period in vitro for E. coli, E. tarda and S. marcescens. In a separate but related study, a partially purified preparation was obtained that was able to bind the ilv leader regions of E. coli, E. tarda, and S. marcescens. Also observed was that a component of this preparation interfered with transcription originating from the P$\sb1$ promoter of the ilvGMEDA operon of E. coli. Results similar to these have been reported to occur within the ilv leader of E. coli in the presence of IHF. Studies to determine the nature of the component (western hybridization, DNA binding assays, and footprint analysis) led to the conclusion that the product being investigated was not IHF but perhaps a novel protein involved in the regulation of the ilv operon. It would appear that although the ilvGMEDA operons of the enteric organisms examined differed in upstream sequence they are regulated by a similar mechanism.

Degree

Ph.D.

Advisors

Umbarger, Purdue University.

Subject Area

Molecular biology

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