ROLE OF ESCHERICHIA-COLI HISTONE-LIKE NUCLEOID-STRUCTURING PROTEIN INBACTERIAL METABOLISM AND STRESS-RESPONSE - IDENTIFICATION OF TARGETS BY 2-DIMENSIONAL ELECTROPHORESIS

The histone-like nucleoid-structuring protein, H-NS, is a major bacter ial chromatin component which influences DNA structure and gene expres sion. Mutations in hns, the structural gene of H-NS protein, have been shown to result in highly pleiotropic effects in Escherichia coli cel ls. In this study, we have initiated an index of the proteins whose sy nthesis is, directly or indirectly regulated by H-NS. Using two-dimens ional gel electrophoresis, we have examined the global changes in gene expression which occured in an hns background compared with its wild- type parent. In addition, we analysed the effects of mutations in two other genes i.e. lrp and pta, which are also involved in global regula tory pathways. Although these comparative analyses revealed several co mmon differences, thus suggesting possible interactions between these regulatory mechanisms, i.e. H-NS, Lrp (leucine-responsive regulatory p rotein) and acetylphosphate, the most extensive modifications occurred in an hns mutant. Among the polypeptides whose level of synthesis was specifically altered in an hns mutant, several corresponded to H-NS t argets previously identified by classical selection methods. Moreover, the present study allows us to characterize several H-NS targets, whi ch were identified either by comparison with the E. coli two-dimension al reference maps or by microsequencing procedure. Many of these newly identified polypeptides are involved in adaptation of E. coli cells t o environmental challenges, and one of them could be involved in bacte rial virulence. Finally, synthesis of several proteins belonging to th e heat-shock regulon, more particularly molecular chaperones, was indu ced in an hns mutant.