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Infection and Immunity, July 2003, p. 3821-3830, Vol. 71, No. 7
0019-9567/03/$08.00+0     DOI: 10.1128/IAI.71.7.3821-3830.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Variable Lipoprotein Genes of Mycoplasma agalactiae Are Activated In Vivo by Promoter Addition via Site-Specific DNA Inversions

Ravenna Flitman-Tene,1 Sigalit Mudahi-Orenstein,1 Sharon Levisohn,2 and David Yogev1*

Department of Membrane and Ultrastructure Research, The Hebrew University-Hadassah Medical School, Jerusalem 91120,1 Mycoplasma Unit, Kimron Veterinary Institute, Beit Dagan 50250, Israel2

Received 2 December 2002/ Returned for modification 25 February 2003/ Accepted 26 March 2003

Mycoplasma agalactiae, the etiological agent of contagious agalactia of small ruminants, has a family of related genes (avg genes) which encode surface lipoprotein antigens that undergo phase variation. A series of 13 M. agalactiae clonal isolates, obtained from one chronically infected animal over a period of 7 months, were found to undergo major rearrangement events within the avg genomic locus. We show that these rearrangements regulate the phase-variable expression of individual avg genes. Northern blot analysis and reverse transcription-PCR showed that only one avg gene is transcribed, while the other avg genes are transcriptionally silent. Sequence analysis and primer extension experiments with two M. agalactiae clonal isolates showed that a specific 182-bp avg 5' upstream region (avg-B2) that is present as a single chromosomal copy serves as an active promoter and exhibits a high level of homology with the vsp promoter of the bovine pathogen Mycoplasma bovis. PCR analysis showed that each avg gene is associated with the avg-B2 promoter in a subpopulation of cells that is present in each subclone. Multiple sequence-specific sites for DNA recombination (vis-like), which are presumably recognized by site-specific recombinase, were identified within the conserved avg 5' upstream regions of all avg genes and were found to be identical to the recombination sites of the M. bovis vsp locus. In addition, a gene encoding a member of the integrase family of tyrosine site-specific recombinases was identified adjacent to the variable avg locus. The molecular genetic basis for avg phase-variable expression appears to be mediated by site-specific DNA inversions occurring in vivo that allow activation of a silent avg gene by promoter addition. A model for the control of avg genes is proposed.

* Corresponding author. Mailing address: Department of Membrane and Ultrastructure Research, The Hebrew University-Hadassah Medical School, Jerusalem, 91120, Israel. Phone: 972-2-6758176. Fax: 972-2-6784010. E-mail: yogev{at}cc.huji.ac.il.

Editor: V. J. DiRita

Infection and Immunity, July 2003, p. 3821-3830, Vol. 71, No. 7
0019-9567/03/$08.00+0     DOI: 10.1128/IAI.71.7.3821-3830.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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