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The parA and parB genes of Pseudomonas aeruginosa are located approximately 8 kb anticlockwise from oriC. ParA is a cytosolic protein present at a level of around 600 molecules per cell in exponential phase, but the level drops about fivefold in stationary phase. Overproduction of full-length ParA or the N-terminal 85 amino acids severely inhibits growth of P. aeruginosa and P. putida. Both inactivation of parA and overexpression of parA in trans in P. aeruginosa also lead to accumulation of anucleate cells and changes in motility. Inactivation of parA also increases the turnover rate (degradation) of ParB. This may provide a mechanism for controlling the level of ParB in response to the growth rate and expression of the parAB operon.The ubiquitous superfamily of Walker-type ATPases is involved in many bacterial processes (7,34,45). One subfamily of these proteins, the ParA proteins, normally functions with a second protein, ParB, and in plasmid systems the combination of ParA and ParB has been associated with better-than-random segregation of low-copy-number plasmids (6,19,23). Although the plasmid partitioning systems fall into two groups on the basis of the ATPase type of component A (type I with Walker-type ATPase and type II with actin-like ATPase), the two groups seem to be unified in the general mechanism of plasmid pairing and directional separation of plasmid molecules prior to cell division. The ParB-like protein binds a centromere-like sequence and is proposed to form pairs of the plasmid molecules (12,17,30,54). The separation of replicons and their transfer towards opposite poles of the dividing cell correlate with the ability of the ParA-like protein to form a dynamic scaffold in the cells (1,3,11,41), its ATPase activity, and its ability to interact with the ParB-parS complex.Duplication of bacterial chromosomes is part of the cell cycle events leading to cell division. Data gathered during the last decade have revealed the role of many different proteins involved in replication and segregation, as well as the spatial and temporal sequence of these processes (4, 14). However, there are still many questions concerning the directional separation of chromosomes to the progeny cells and the regulation of this process. The discovery of highly conserved homologues of ParA (Walker-type ATPase) and ParB encoded by bacterial chromosomes in close vicinity to oriC (5, 18, 36, 44, 47) suggested a role for these proteins in chromosome segregation. To date, the potential roles of both the ParA and ParB proteins in cell biology have been related to regulatory cell cycle check points (8,16,37,44,48,49), positioning of oriC domains (38, 50), separation of replicated origins (37), and the translocation of the proteins to fixed cell locations (55, 61). Studies on chromosomal ParA and ParB also revealed a lack of uniformity in their action in different organisms despite the high degree of conservation at the levels of sequence and genetic organization (5,20,21,26,32,40,44,55,56,60).The aim of the work described in th...

CBA mice infected with the helminthSchistosomamansonidevelop severe CD4 T cell-mediated hepaticgranulomatous inflammation against parasite eggs associated with a robust Th17 cell response.We investigated the requisites for Th17 cell development using novel CD4 T cells expressing a transgenic (Tg) TCR specific for the major Sm-p40 egg Ag, which produce IL-17 when stimulated with live schistosome eggs. Neutralization of IL-23 or blockade of the IL-1 receptor, but not IL-6 neutralization, abrogated egg-induced IL-17 secretion by Tg T cells, whereas exogenous IL-23 or IL-1β reconstituted their ability to produce IL-17 stimulated by syngeneic IL-12p40-deficient DCs. Kinetic analysis demonstrated that IL-17 production was initiated by IL-23 and amplified by IL-1β. Significantly, schistosome-infected IL-12p40-deficientor IL-1R antagonist treated CBA mice developed markedly reduced hepatic immunopathologywith a dampened egg Ag-specific IL-17 response. These results demonstrate the IL-23-IL-1-IL-17 axis to play a central role in the development of severe schistosome egg-induced immunopathology.

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Pseudomonas aeruginosa ParA belongs to a large subfamily of Walker-type ATPases acting as partitioning proteins in bacteria. ParA has the ability to both self-associate and interact with its partner ParB. Analysis of the deletion mutants defined the part of the protein involved in dimerization and interactions with ParB. Here, a set of ParA alanine substitution mutants in the region between E67 and L85 was created and analysed in vivo and in vitro. All mutants impaired in dimerization (substitutions at positions M74, H79, Y82 and L84) were also defective in interactions with ParB, suggesting that ParA–ParB interactions depend on the ability of ParA to dimerize. Mutants with alanine substitutions at positions E67, C68, L70, E72, F76, Q83 and L85 were not impaired in dimerization, but were defective in interactions with ParB. The dimerization interface partly overlapped the pseudo-hairpin, involved in interactions with ParB. ParA mutant derivatives tested in vitro showed no defects in ATPase activity. Two parA alleles (parA84, whose product can neither self-interact nor interact with ParB, and parA67, whose product is impaired in interactions with ParB, but not in dimerization) were introduced into the P. aeruginosa chromosome by homologous gene exchange. Both mutants showed defective separation of ParB foci, but to different extents. Only PAO1161 parA84 was visibly impaired in terms of chromosome segregation, growth rate and motility, similar to a parA-null mutant.