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Sökning: WFRF:(Herman Antosiewicz A)

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2.
  • Baranska, S., et al. (författare)
  • Regulation of the switch from early to late bacteriophage lambda DNA replication
  • 2001
  • Ingår i: Microbiology. - : Microbiology Society. - 1350-0872 .- 1465-2080. ; 147, s. 535-547
  • Tidskriftsartikel (refereegranskat)abstract
    • There are two modes of bacteriophage lambda DNA replication following infection of its host, Escherichia coli. Early after infection, replication occurs according to the theta (theta or circle-to-circle) mode, and is later switched to the sigma (sigma or rolling-circle) mode. It is not known how this switch, occurring at a specific time in the infection cycle, is regulated. Here it is demonstrated that in type cells the replication starting from ori lambda proceeds both bidirectionally and unidirectionally, whereas in bacteria devoid of a functional DnaA protein, replication from ori lambda is predominantly unidirectional. The regulation of directionality of replication from ori lambda is mediated by positive control of lambda p(R) promoter activity by DnaA, since the mode of replication of an artificial lambda replicon bearing the p(tet) promoter instead of p(R) was found to be independent of DnaA function. These findings and results of density-shift experiments suggest that in dnaA mutants infected with lambda, phage DNA replication proceeds predominantly according to the unidirectional theta mechanism and is switched early after infection to the sigma mode. It is proposed that in wild-type E. coli cells infected with lambda, phage DNA replication proceeds according to a bidirectional theta mechanism early after infection due to efficient transcriptional activation of ori lambda, stimulated by the host DnaA protein. After a few rounds of this type of replication, the resulting increased copy number of lambda genomic DNA may cause a depletion of free DnaA protein because of its interaction with the multiple DnaA-binding sites in lambda DNA. It is proposed that this may lead to inefficient transcriptional activation of ori lambda resulting in unidirectional theta replication followed by sigma type replication.
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3.
  • Gabig-Ciminska, Magdalena, et al. (författare)
  • The cell surface protein Ag43 facilitates phage infection of Escherichia coli in the presence of bile salts and carbohydrates
  • 2002
  • Ingår i: Microbiology. - : Microbiology Society. - 1350-0872 .- 1465-2080. ; 148, s. 1533-1542
  • Tidskriftsartikel (refereegranskat)abstract
    • it was found that infection of Escherichia coli by bacteriophage lambda is inhibited in the presence of certain bile salts and carbohydrates when cells are in the 'OFF' state for production of the phase-variable cell surface protein antigen 43 (Ag43). The inhibition of phage growth was found to be due to a significant impairment in the process of phage adsorption. Expression of the gene encoding Ag43 (agn43) from a plasmid or inactivation of the oxyR gene (encoding an activator of genes important for defence against oxidative stress) suppressed this inhibition. A mutation, rpoA341, in the gene encoding the alpha subunit of RNA polymerase also facilitated phage adsorption in the presence of bile salts and carbohydrates. The rpoA341 mutation promoted efficient production of Ag43 in a genetic background that would otherwise be in the 'OFF' phase for expression of the agn43 gene. Analysis of a reporter gene fusion demonstrated that the promoter for the agn43 gene was more active in the rpoA341 mutant than in the otherwise isogenic rpoA(+) strain. The combined inhibitory action of bile salts and carbohydrates on phage adsorption and the abolition of this inhibition by production of Ag43 was not restricted to lambda as a similar phenomenon was observed for the coliphages P1 and T4.
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