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Infection and Immunity, September 2005, p. 5568-5577, Vol. 73, No. 9
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.9.5568-5577.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Rate of Inversion of the Salmonella enterica Shufflon Regulates Expression of Invertible DNA

Connie K. P. Tam,* Jim Hackett, and Christina Morris

Department of Biochemistry, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China

Received 9 November 2004/ Returned for modification 20 January 2005/ Accepted 20 April 2005

Salmonella enterica serovar Typhi and some strains (Vi+) of serovar Dublin use type IVB pili to facilitate bacterial self-association, but only when the PilV proteins (potential minor pilus proteins) are not synthesized. Pilus-mediated self-association may be important in the pathogenesis of enteric fever. We have suggested that the rate of Rci-catalyzed inversion of DNA encoding the C-terminal portions of the PilV proteins controls PilV protein synthesis. This potentially represents a novel means of transcriptional control. Here, it is initially shown that DNA inversion per se is required for inhibition of gene expression from invertible DNA. Binding, without DNA scission, of Rci to its substrate sequences on DNA cannot explain the data obtained. Next, it is shown that inversion frequencies of xylE-encoding DNA, bracketed by Rci substrate sequences, may be modulated by changes in the 19-bp consensus sequences which are essential components of Rci substrate DNA. The affinity of Rci for these sequences affects inversion frequencies, so that a greater affinity is predictive of faster inversion, and therefore less synthesis of product encoded by invertible DNA. Inversion events may inhibit transcription of DNA from external promoters. In vivo, the frequency of Rci-mediated inversion is influenced by the extent of DNA supercoiling, with increasing levels of expression of invertible genes as novobiocin inhibits DNA supercoiling and thus Rci action. This inhibition of DNA supercoiling results in increased synthesis of PilV proteins as Rci activity decreases, and, in turn, bacterial self-association (particularly in serovar Dublin) decreases.

* Corresponding author. Mailing address: Department of Biochemistry, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China. Phone: 852-2358-7275. Fax: 852-2719-8158. E-mail: pinecone{at}ust.hk.

Editor: V. J. DiRita

Infection and Immunity, September 2005, p. 5568-5577, Vol. 73, No. 9
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.9.5568-5577.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Tam, C. K. P., Morris, C., Hackett, J. (2006). The Salmonella enterica Serovar Typhi Type IVB Self-Association Pili Are Detached from the Bacterial Cell by the PilV Minor Pilus Proteins. Infect. Immun. 74: 5414-5418 [Abstract] [Full Text]  


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