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Journal of Bacteriology, January 2001, p. 557-569, Vol. 183, No. 2
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.2.557-569.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

ihfA Gene of the Bacterium Myxococcus xanthus and Its Role in Activation of Carotenoid Genes by Blue Light

Alberto J. Moreno, Marta Fontes, and Francisco J. Murillo*

Departamento de Genética y Microbiología, Facultad de Biología, Universidad de Murcia, 30100 Murcia, Spain

Received 8 August 2000/Accepted 20 October 2000

Myxococcus xanthus responds to blue light by producing carotenoids. Several regulatory genes are known that participate in the light action mechanism, which leads to the transcriptional activation of the carotenoid genes. We had already reported the isolation of a carotenoid-less, Tn5-induced strain (MR508), whose mutant site was unlinked to the indicated regulatory genes. Here, we show that Omega MR508::Tn5 affects all known light-inducible promoters in different ways. It blocks the activation of two of them by light but makes the activity of a third one light independent. The Omega MR508 locus has been cloned and sequenced. The mutation had occurred at the promoter of a gene we propose is the M. xanthus ortholog of ihfA. This encodes the alpha  subunit of the histone-like integration host factor protein. An in-frame deletion within ihfA causes the same effects as the Omega MR508::Tn5 insertion. Like other IhfA proteins, the deduced amino acid sequence of M. xanthus IhfA shows much similarity to HU, another histone-like protein. Sequence comparison data, however, and the finding that the M. xanthus gene is preceded by gene pheT, as happens in other gram-negative bacteria, strongly argue for the proposed orthology relationship. The M. xanthus ihfA gene shows some unusual features, both from structural and physiological points of view. In particular, the protein is predicted to have a unique, long acidic extension at the carboxyl terminus, and it appears to be necessary for normal cell growth and even vital for a certain wild-type strain of M. xanthus.

* Corresponding author. Mailing address: Departamento de Genetica y Microbiologia, Facultad de Biologia, Universidad de Murcia, Apdo. 4021, 30100 Murcia, Spain. Phone: 34-968-36-49-51. Fax: 34-968-36-39-63. E-mail: araujo{at}um.es.

Journal of Bacteriology, January 2001, p. 557-569, Vol. 183, No. 2
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.2.557-569.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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