Mechanisms of Differential Expression of ESX-1 Secretion System Genes in Mycobacterium smegmatis

Peters, Ryan G.

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Mechanisms of Differential Expression of ESX-1 Secretion System Genes in Mycobacterium smegmatis

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An important strategy employed by Mycobacterium tuberculosis (Mtb) to evade the host immune system is to escape from phagosomes into the cytoplasm of macrophages. To accomplish this and other goals, Mtb secretes various virulence factors through several secretion systems. One such system, ESX-1, is necessary to escape the host phagosome. In particular, EsxA and EsxB are proteins secreted by the ESX-1 system that are important for disrupting the phagosomal membrane. These proteins appear to be encoded in a four-gene operon in the ESX-1 locus. However, previous work has shown that mRNA abundance differs between genes in this supposed operon, in a way that cannot be explained by the known transcription start site (TSS) and endoribonuclease cleavage site. Here we search for additional promotors in this PE35-PPE68-esxB-esxA locus and examine the contribution of each TSS and cleavage site to mRNA expression. Using the model organism Mycobacterium smegmatis, we characterize a series of mutaitons by quantitative PCR and 5’ rapid amplification of cDNA ends. We map two promotors that contribute to expression of esxB-A, an mRNA cleavage site upstream of esxB, and suggest that at least one additional promotor is present in the locus. These data lay the foundation for a better understanding of the mechanisms behind differential expression of ESX-1 genes in mycobacteria.

This report represents the work of one or more WPI undergraduate students submitted to the faculty as evidence of completion of a degree requirement. WPI routinely publishes these reports on its website without editorial or peer review.

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