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The Single Extracytoplasmic-Function Sigma Factor of Xylella fastidiosa Is Involved in the Heat Shock Response and Presents an Unusual Regulatory Mechanism

Departamento de Microbiologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, Av. Prof. Lineu Prestes 1374, 05508-900 São Paulo, SP, Brazil,¹ Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes 748, 05508-900 São Paulo, SP, Brazil²

Received 6 July 2006/ Accepted 26 October 2006

Genome sequence analysis of the bacterium Xylella fastidiosa revealed the presence of two genes, named rpoE and rseA, predicted to encode an extracytoplasmic function (ECF) sigma factor and an anti-sigma factor, respectively. In this work, an rpoE null mutant was constructed in the citrus strain J1a12 and shown to be sensitive to exposure to heat shock and ethanol. To identify the X. fastidiosa ^E regulon, global gene expression profiles were obtained by DNA microarray analysis of bacterial cells under heat shock, identifying 21 ^E-dependent genes. These genes encode proteins belonging to different functional categories, such as enzymes involved in protein folding and degradation, signal transduction, and DNA restriction modification and hypothetical proteins. Several putative ^E-dependent promoters were mapped by primer extension, and alignment of the mapped promoters revealed a consensus sequence similar to those of ECF sigma factor promoters of other bacteria. Like other ECF sigma factors, rpoE and rseA were shown to comprise an operon in X. fastidiosa, together with a third open reading frame (XF2241). However, upon heat shock, rpoE expression was not induced, while rseA and XF2241 were highly induced at a newly identified ^E-dependent promoter internal to the operon. Therefore, unlike many other ECF sigma factors, rpoE is not autoregulated but instead positively regulates the gene encoding its putative anti-sigma factor.

Published ahead of print on 10 November 2006.

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