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Genetic analysis of the Salmonella transcription factor HilA

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HilA, a Salmonella transcription factor, activates the invF-1 and prgH promoters through binding to the HilA box, which contains 2 copies of a TTKHAT motif separated by a T centered at -45 relative to the start sites of transcription. The N-terminal 112 amino acids of HilA are similar to winged helix-turn-helix DNA binding/transcription activation domains (wHTH DBDs). The remaining 441 amino acids are not similar in sequence to any other well-characterized transcription factors. Here, we report that the wHTH DBD is essential for activation of both promoters, but amino acids 113-554 are only required for normal activation of invF-1. Some alanine substitutions in the putative α loop, which connects the recognition and positioning helices in wHTH DBDs, cause a loss-of-activation phenotype. A hilA allele encoding a protein with an alanine substituted for arginine at position 71 in the α loop has a loss-of-activation defect exclusively at the prgH promoter. The results suggest distinct roles for one or more domains formed by amino acids 113-554 and for arginine 71 in activation of the 2 promoters.

HilA, un facteur de transcription de Salmonella, active les promoteurs invF-1 et prgH par sa liaison à la boîte HilA qui contient 2 copies d’un motif TTKHAT séparées par un T centré à la position -45 relativement aux sites d’initiation de la transcription. Les 112 acides aminés N-terminaux de HilA sont similaires aux domaines de liaison de l’ADN et d’activation de la transcription hélice-tour-hélice « winged » (wHTH DBDs). Les 441 autres acides aminés ne sont similaires à la séquence d’aucun facteur de transcription connu. Nous rapportons ici que le wHTH DBD est essentiel à l’activation des deux promoteurs mais que les acides aminés 113-554 sont les seuls qui sont requis à l’activation normale d’ invF-1. Quelques substitutions d’alanine dans la boucle α présumée, qui entre établit le contact entre les hélices de reconnaissance et de positionnement du wHTH DBDs, produisent un phénotype de perte d’activation. Un allèle hilA codant une protéine comportant une alanine en substitution à une arginine à la position 71 de la boucle α possède un défaut d’activation envers le promoteur prgH seulement. Ces résultats suggèrent qu’un ou plusieurs domaines formés par les acides aminés 113-554 et l’arginine 71 jouent des rôles distincts dans l’activation des 2 promoteurs.

Document Type: Research Article

Publication date: October 1, 2008

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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