Abstract
SigD and SigE (Salmonella invasion gene) are proteins needed for optimal invasion of Salmonella typhimurium into eukaryotic cells in vitro. SigD is a secreted protein and SigE is a putative chaperone required for SigD stability and/or secretion. SigD is secreted by a type III secretion apparatus encoded within a pathogenicity island on the Salmonella chromosome known as Salmonella pathogenicity island 1 (SPI1). The expression of sigDE, which is not linked to SPI1, is co-ordinately regulated with the SPI1 genes and is dependent on the transcriptional regulators SirA, HilA and InvF. These three proteins alone are unable to activate transcription from the sigD promoter in Escherichia coli, therefore it is likely that other factors are needed for expression. A screen for genes required for the expression of a sigD-lacZYA reporter fusion found a mutant with a transposon insertion in spaS, an SPI1 gene which encodes a putative inner-membrane component of the type III secretion system. The expression of a SPI1 operon encoding a putative chaperone (SicA) and several secreted proteins (Sips B, C, D and A) was also reduced in this mutant. The regulation defect of the spaS mutant was complemented by sicA and not by spaS. Because sicA is encoded immediately downstream of spaS, the mutation in spaS was likely to be polar on the expression of sicA. In addition, a sicA disruption mutant was as defective as an invF deletion mutant for the expression of sigD, sicA and sipC reporter fusions. The introduction of plasmids encoding invF and sicA into a non-pathogenic E. coli K-12 strain stimulated the transcription of both a sicA- and a sigD-lacZYA promoter fusion. This result suggests that InvF and SicA are sufficient for the expression of these genes. This is the first demonstration of a positive regulatory role for a putative type III secretion system chaperone in the expression of virulence genes.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
