The transcriptional activator HIyU of Vibrio cholerae: nucleotide sequence and role in virulence gene expression

Abstract
HlyU upregulates expression of the haemolysin, HlyA, of Vibrio cholerae. DNA sequence analysis indicates that HlyU is an 11.9 kDa protein containing a putative helix-turn-helix motif and belonging to a family of small regulatory proteins, including NolR (Rhizobium meliloti), SmtB (Synechococcus PCC 7942) and ArsR (piasmids R773, Escherichia coli; p1258, Staphylococcus aureus; and pSX267, Staphylococcus xylosus). An hlyU mutant was constructed by insertional inactivation, and found to be deficient in the production of both the haemolysin and a 28kDa secreted protein. The mutant was assessed for virulence in the infant mouse cholera model, revealing a 100-fold increase in the LD50.. This suggests that HlyU promotes expression of virulence determinant(s) in vivo.

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