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Transcriptional organization and regulation of the Escherichia coli K30 group 1 capsule biosynthesis ( cps ) gene cluster
Author(s) -
Rahn Andrea,
Whitfield Chris
Publication year - 2003
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2003.03354.x
Subject(s) - biology , operon , gene , transcription (linguistics) , gene cluster , escherichia coli , promoter , lac operon , genetics , antitermination , transcriptional regulation , transcription factor , gene expression , linguistics , philosophy
Summary Escherichia coligroup 1 capsules are important virulence determinants, yet little is known about the transcriptional organization or regulation of their biosynthetic (cps) operons. Transcription of the prototype serotype K30 cluster is modulated by the JUMPStart–RfaH antitermination mechanism, with thecpspromoter being localized to a region immediately upstream of the JUMPStart sequence. A putative stem–loop structure located within the K30cpscluster separates conserved genes with products that are required for surface expression of capsule from serotype‐specific genes encoding enzymes for polymer repeat‐unit synthesis and polymerization. This putative stem–loop structure significantly reduces transcription in a termination‐probe vector and may contribute to differential expression of thecpsgenes. Previous work indicated that increased amounts of group 1 capsular polysaccharide synthesis resulted from the overexpression of the Rcs (regulator ofcapsulesynthesis) proteins. However, neither overexpression of the transcriptional activator RcsB nor anrcsB::aadAchromosomal insertion altered the level of transcription measured bycps::lacZfusions. In the group 1 strains examined, an RcsAB box was found immediately upstream ofgalF, a gene involved in the production of sugar nucleotide precursors. Overexpression of RcsB was found to result in a threefold increase in transcription of agalF::lacZchromosomal fusion. Moreover, overexpression of GalF gave rise to a two‐ to threefold increase in cell‐free as well as cell‐associated capsule, without affectingcps::lacZactivity. These results indicate that transcription of theE. coligroup 1 capsule cluster itself is not regulated by the Rcs system and may, in fact, be constitutive. However, the Rcs system can potentially influence levels of capsular polysaccharide production by increasinggalF transcription and influencing the available pool of biosynthetic precursors.