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Giardia lamblia undergoes antigenic variation of variant-specific surface proteins (VSPs) that are encoded by a family of ~150 vsp genes only one of which is expressed at a time. The vsp gene promoters have not been previously studied. A comparison of the upstream non-coding region of vsp genes shows that they lack the AT-rich regions found in other Giardia gene promoters. We have determined that the core promoters of vsp A6 and vsp C5 genes extend from -57 to + 6 and -50 to + 6 respectively. Through linker scanning analysis, we have also identified regions within the vsp A6 core promoter important for promoter activity that span -7-3, -12-8, -17-13 and -42-38.There is no sequence similarity in the upstream regions of the previously characterized vsp genes that were analyzed, with the exception of a seven nucleotide region that encompasses the translation initiation site: Py A A T G T T. We have demonstrated that the four nucleotides flanking the start codon are essential for promoter activity. This result suggests that it may be an Inr element, which by definition determines the site of transcription initiation. In addition, this element loosely resembles the metazoan Inr consensus: Py Py A A/T Py Py. Using 5′ RACE I have determined that for two vsp genes, the translation and transcription start sites are synonymous and reside within this conserved element. However, we were unable to identify protein factors that bind this region using electrophoretic mobility shift assays.A search for characteristic VSP motifs, such as CRGKA, amongst identified ORFs in the Giardia genome assembly in turn identified 180 ORFs which may be VSPs. Eighty one of these are found within contigs while 99 of these are found at contig and 80 ORFs have the Inr element identified in this study.This study supports the hypothesis that longer upstream non-coding regions of vsp genes play a role in regulating the expression of these genes and hence antigenic variation in G. lamblia.

Interest in the study of antiviral substances stems from the fact that classical chemotherapy as it is known in bacterial diseases has thus far not been successful in the field of viral diseases. However, any proven antiviral agent is a potential drug against virus infection. Although the ultimate goal of effective chemotherapy of virus infections may or may not be attained, information concerning such substances may provide clues to the nature of host-virus interactions and help to elucidate the patterns of the pathogenesis of virus diseases (Zimmermann and Schafer, 1960; Melnick and Rapp, 1965) and also to afford tools for the classification of viruses (Tamm and Eggers, 1962; Barry et al., 1962). [...]

The Citrobacter rodentium genome sequence contains a phoPQ operonhomologous (~79% identity) to that of S. typhimurium. We report that C. rodentiumPhoQ senses fluctuations in Mg2+ concentrations and acidic pH. Surprisingly, PhoQwas not activated by the presence of AMPs. However, activation by AMPs is observedwhen C. rodentium PhoP/PhoQ was expressed in as. typhimurium background. Weidentified an outer membrane protease of the omptin family that was responsible forinhibiting PhoQ activation by AMPs. In stark contrast to S. typhimurium, which relieson LPS modifications to resist AMPs, our results suggest that C. rodentium promotesresistance through a PhoP/PhoQ-dependent OM protease to inhibit disruption of theouter membrane by AMPs . / La séquence du génome de Citrobacter rodentium présente un opéron phoPQ(~79% identité) homologue à celui de S. typhimurium. Nous avons déterminé quePhoQ de C. rodentium perçoit les variations de pH et en Mg2+ du milieu environnant.De manière surprenante, les PAMs ne causent aucune augmentation d'activité dePhoQ. Néeanmoins, lorsque le système PhoP/PhoQ de C. rodentium est exprimé chezS. typhimurium les PAMs activent PhoQ. Nous avons identifié une protéine de lamembrane externe appartenant à la famille des omptin qui est responsable del'inactivité de PhoQ en présence des P AMs. Ces résultats suggèrent que le mécanismede résistance aux PAMs de C. rodentium serait régulé par le système PhoP/PhoQ et une protéase qui empêcherait la destruction de la membrane externe par les P AMs. Cemécanisme de défense est différent de celui du système PhoP/PhoQ de S. typhimuriumqui repose essentiellement sur des modification du LPS .

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