Alkaline phosphatase regulation by the σS factor of RNA polymerase in Escherichia coli.

Author(s)

Natalia Pasternak Taschner

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Ciências Biomédicas (ICB/SDI)
• Defense date: 2006-05-31

Examining board members

Beny Spira; Regina Lúcia Baldini; Marilis do Valle Marques; Carlos Frederico Martins Menck; Aline Maria da Silva

• Advisor: Beny Spira

Abstract

In E. coli, the RNA polymerase associated with &#963S (E&#963S) is responsible for the transcription of the majority of the genes related to survival during stress periods or during the stationary phase of growth. When cells enter a phase of phosphate starvation, the transcription of several genes and operons, known as the PHO regulon, is activated. Knock-out of rpoS, which encodes &#963S, increases the expression of most PHO genes. The negative effect of &#963S on PHO expression is probably due to the competition between &#963S and &#963D for the core RNA polymerase. Unlike all other PHO genes, pstS, the first gene of the pst operon, was mildly stimulated by &#963S. The promoter region of pstS contains a cytosine residue at position -13, and an IHF binding site. These elements are known to be important for the transcription of &#963S-dependent genes, and may contribute for the transcription of pstS by E&#963S . The polymorphism of rpoS in several E. coli K-12 strains was evaluated. An amber mutation in codon 33 of this gene was found in 2 out of 7 strains. These strains were found to suppress the amber mutation and to produce a normal 38 KDa &#963S protein. Non-suppressor strains carrying this amber mutation produced a &#963S variant, lacking 55 amino acids. The truncated &#963S protein was still able to drive the transcription of its dependent genes, albeit in a smaller proportion. Strains carrying the rpoS amber mutation presented a distinct phenotype regarding the expression of the PHO regulon genes. (AU)