Sialic acid transport and catabolism are cooperatively regulated by SiaR and CRP in nontypeable Haemophilus influenzae

Jason W. Johnston, Haider Shamsulddin, Anne Frances Miller, Michael A. Apicella

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


Background. The transport and catabolism of sialic acid, a critical virulence factor for nontypeable Haemophilus influenzae, is regulated by two transcription factors, SiaR and CRP. Results. Using a mutagenesis approach, glucosamine-6-phosphate (GlcN-6P) was identified as a co-activator for SiaR. Evidence for the cooperative regulation of both the sialic acid catabolic and transport operons suggested that cooperativity between SiaR and CRP is required for regulation. cAMP was unable to influence the expression of the catabolic operon in the absence of SiaR but was able to induce catabolic operon expression when both SiaR and GlcN-6P were present. Alteration of helical phasing supported this observation by uncoupling SiaR and CRP regulation. The insertion of one half-turn of DNA between the SiaR and CRP operators resulted in the loss of SiaR-mediated repression of the transport operon while eliminating cAMP-dependent induction of the catabolic operon when GlcN-6P was present. SiaR and CRP were found to bind to their respective operators simultaneously and GlcN-6P altered the interaction of SiaR with its operator. Conclusions. These results suggest multiple novel features for the regulation of these two adjacent operons. SiaR functions as both a repressor and an activator and SiaR and CRP interact to regulate both operons from a single set of operators.

Original languageEnglish
Article number240
JournalBMC Microbiology
StatePublished - 2010

Bibliographical note

Funding Information:
This work was supported by funding from NIAID Grants AI024616 and AI30040 and NIH grant GM085302.

ASJC Scopus subject areas

  • Microbiology
  • Microbiology (medical)


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