Abstract
Enterohaemorrhagic Escherichia coli O157:H7 (EHEC) carries a pathogenic island LEE that is consisted mainly of five polycistronic operons. In the lee3 operon, mpc is the first gene and has been reported to down regulate the type-3 secretion system of EHEC when its gene product is over-expressed. Furthermore, mpc has been suggested to have a regulation function via translation but the mechanism remains unclear. To clarify this hypothesis, we dissected the polycistron and examined the translated products. We conclude that translation of mpc detrimentally governs the translation of the second gene, escV, which in turn affects the translation of the third gene, escN. Then sequentially, escN affects the expression of the downstream genes. Furthermore, we located a critical cis element within the mpc open-reading frame that plays a negative role in the translation-dependent regulation of lee3. Using qRT-PCR, we found that the amount of mpc RNA transcript present in EHEC was relatively limited when compared to any other genes within lee3. Taken together, when the transcription of LEE is activated, expression of mpc is tightly controlled by a restriction of the RNA transcript of mpc, translation of which is then critical for the efficient production of the operon’s downstream gene products.
Highlights
Enterohaemorrhagic Escherichia coli (EHEC) is a food-borne bacterium that causes abdominal cramps, diarrhea and haemorrhagic colitis
To children and the elderly, the infection may further develop into hemolytic uremic syndrome (HUS) and lead to serious renal failure and hemolytic anemia [1]
To understand how the regulation mechanism of mpc acting on lee3 in details, we first created three constructs (Fig 1A, upper panel) that carried escV, escV along with upstream mpc, and escV along with start-codon-altered mpc in order to compare the expression levels of EscV under these three settings
Summary
Enterohaemorrhagic Escherichia coli (EHEC) is a food-borne bacterium that causes abdominal cramps, diarrhea and haemorrhagic colitis. To children and the elderly, the infection may further develop into hemolytic uremic syndrome (HUS) and lead to serious renal failure and hemolytic anemia [1]. Ingestion of contaminated food is the most common reason for EHEC infection. The cattle intestine is regarded as the main reservoir of EHEC, a reasoning that pinpoints raw or under-cooked ground beef and raw milk as frequent sources of EHEC infection outbreaks. This bacterium is increasingly being identified as associated with contaminated fruits and vegetables [1,2,3].
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