Peter Olsén

The Pai-associated leuX specific tRNA5(Leu) affects type 1 fimbriation in pathogenic Escherichia coli by control of FimB recombinase expression.

The uropathogenic Escherichia coli strain 536 (O6:K15: H31) carries two large chromosomal pathogenicity islands (Pais). Both Pais are flanked by tRNA genes. Spontaneous deletion of Pai II results in truncation of the leuX tRNALeu5 gene. This tRNA is required for the expression of type 1 fimbriae (Fim) and other virulence factors. Transcription of fimA, encoding the major type 1 fimbrial subunit is controlled by an invertable DNA switch. The inversion is catalysed by two recombinases, FimB and FimE. FimB is able to turn the switch on, FimE only off. The fimB gene of strain 536 contains five TTG codons recognized by tRNALeu5, fimE contains only two. It was proposed that turning on the fim switch requires efficient translation of FimB, in turn requiring tRNALeu5. Strains in which the TTG codons in fimB were replaced with CTG codons at the wild‐type locus were able to produce type 1 fimbriae in the absence of leuX. fimB transcription was influenced by the presence of leuX, but only slightly affected by the presence or absence of leuX codons in fimB. FimB translation was significantly higher from codon‐replaced fimB genes than that of wild‐type fimB genes in various strain backgrounds. The fim switch was shown to be switched off in leuX − derivatives of E. coli 536, but could be found in the on position when the codon‐altered fimB gene was exchanged into the chromosome of these strains. From these data, it is apparent that tRNALeu5 is required for efficient translation of FimB, in turn, leading to type 1 fimbrial expression.

ORIENTATION-DEPENDENT ENHANCEMENT BY H-NS OF THE ACTIVITY OF THE TYPE 1 FIMBRIAL PHASE SWITCH PROMOTER IN ESCHERICHIA COLI

Abstract Phase variation of type 1 fimbriation in Escherichia coli is associated with the inversion of a 314-bp DNA element, positioned proximal to and upstream of fimA, which encodes the major type 1 fimbrial subunit. This DNA switch region contains a promoter that drives transcription of fimA only when the switch is in the ON orientation. Using chromosomal and plasmid-borne lacZ reporter cassettes, we show here how the global regulator H-NS affects the activity of the fimA promoter. In phase-locked reporter cassettes the activity of the fimA promoter was found to be enhanced in a hns-positive background, but only when the switch was in the ON orientation. Also, the number of fimbriae produced by a phase-locked ON strain was significantly higher in a hns-positive background. By means of competitive gel retardation and DNase I protection assays, H-NS binding to DNA segments adjacent to and within the phase switch region was demonstrated.

Strategic Management and the Politics of Production in the Development of Work: A Case Study in a Danish Electronic Manufacturing Plant

After presenting different conceptions of work politics in industrial sociology and sociology of organization, the authors argue that changes in work and technology, and hence the politics of work, may be better comprehended through a concept of the social constitution of the company. Subsequently, this concept is used as a theoretical and methodological basis for an in-depth case study of the processes of social change connected with the introduction of semi-autonomous working groups in a Danish electronic manufacturing plant. It is shown that the historically developed norms and culture of the organization - referred to here as the social constitution of the company - contribute to the creation of profound, ambivalent attitudes among management as well as workers towards more fundamental changes of work content and organization. Finally, the implications for strategic management for the development of work at the company level are discussed.