@phdthesis{Froehlich2012,
  author    = {Fr{\"o}hlich, Kathrin},
  title     = {Assigning functions to Hfq-dependent small RNAs in the model pathogen Salmonella Typhimurium},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-85488},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2012},
  abstract  = {Non-coding RNAs constitute a major class of regulators involved in bacterial gene expression. A group of riboregulators of heterogeneous size and shape referred to as small regulatory RNAs (sRNAs) control trans- or cis-encoded genes through direct base-pairing with their mRNAs. Although mostly inhibiting their target mRNAs, several sRNAs also induce gene expression. An important co-factor for sRNA activity is the RNA chaperone, Hfq, which is able to rearrange intramolecular secondary structures and to promote annealing of complementary RNA sequences. In addition, Hfq protects unpaired RNA from degradation by ribonucleases and thus increases sRNA stability. Co-immunoprecipitation of RNA with the Hfq protein, and further experimental as well as bioinformatical studies performed over the last decade suggested the presence of more than 150 different sRNAs in various Enterobacteria including Escherichia coli and Salmonellae. So-called core sRNAs are considered to fulfill central cellular activities as deduced from their high degree of conservation among different species. Approximately 25 core sRNAs have been implicated in gene regulation under a variety of environmental responses. However, for the majority of sRNAs, both the riboregulators' individual biological roles as well as modes of action remain to be elucidated. The current study aimed to define the cellular functions of the two highly conserved, Hfq-dependent sRNAs, SdsR and RydC, in the model pathogen Salmonella Typhimurium. SdsR had been known as one of the most abundant sRNAs during stationary growth phase in E. coli. Examination of the conservation patterns in the sdsR promoter region in combination with classic genetic analyses revealed SdsR as the first sRNA under direct transcriptional control of the alternative σ factor σS. In Salmonella, over-expression of SdsR down-regulates the synthesis of the major porin OmpD, and the interaction site in the ompD mRNA coding sequence was mapped by a 3'RACE-based approach. At the post-transcriptional level, expression of ompD is controlled by three additional sRNAs, but SdsR plays a specific role in porin regulation during the stringent response. Similarly, RydC, the second sRNA adressed in this study, was initially discovered in E. coli but appeared to be conserved in many related γ-proteobacteria. An interesting aspect of this Hfq-dependent sRNAs is its secondary structure involving a pseudo-knot configuration, while the 5' end remains single stranded. A transcriptomic approach combining RydC pulse-expression and scoring of global mRNA changes on microarrays was employed to identify the targets of this sRNA. RydC specifically activated expression of the longer of two versions of the cfa mRNA encoding for the phospholipid-modifying enzyme cyclopropane fatty acid synthase. Employing its conserved single-stranded 5' end, RydC acts as a positive regulator and masks a recognition site of the endoribonuclease, RNase E, in the cfa leader.},
  subject      = {Small RNA},
  language  = {en}
}
@article{HackerHofHughesetal.1985,
  author    = {Hacker, J{\"o}rg and Hof, H. and Hughes, C. and Goebel, W.},
  title     = {Salmonella typhimurium strains carrying hemolysin plasmids and cloned hemolysin. genes from Escherichia coli},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-40309},
  year      = {1985},
  abstract  = {Like all other Salmonella typhimurium strains examined, the smooth variants SF1397 (L T2) and 1366 and also their semi-rough and rough derivatives are non-haemolytic. Nevertheless, two haemolysin (Hly) plasmids of E. coli belonging to the inc groups incFllI,lv (pSU316) and incIz (pHly152) were able to be introduced into these strains by conjugation and stably maintained. A considerable percentage of the Hly+ transconjugants obtained had lost parts of their O-side chains, a result of selection for the better recipient capability of « semi-rough» variants rather than the direct influence of the Hly+ plasmids themselves. In contrast to the incF1lI1V plasmid pSU316, which exhibited higher conjugation rates with rough recipients, the incIz plasmid pHly152 was accepted best by smooth strains. Transformation with cloned E. coli haemolysin (hly) determinant was inefficient ( <10-8) for smooth strains, but 102-103 times higher for rough recipients, and was increased by the use of Salmonella-modified DNA. The transform ants and transconjugants were relatively stable and showed the same haemolytic activity as the E. coli donor strains. The virulence of the Hly+ smooth, semi-rough and rough S. typhimurium strains was tested in two mouse models, and neither the mortality rate nor the ability to multiply within the mouse spleen was influenced by the hly determinants.},
  language  = {en}
}
@article{HofEmmerlingHackeretal.1982,
  author    = {Hof, H. and Emmerling, P. and Hacker, J{\"o}rg and Hughes, C.},
  title     = {The role of macrophages in primary and secondary infection of mice with Salmonella typhimurium},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-40248},
  year      = {1982},
  abstract  = {Elimination of macrophages with high-molecular dextran sulphate (OS) markedly impairs resistance of mice to primary infection with smooth, virulent strains of Salmonella typhimurium, whereas stimulation of this system by killed Bordetella pertussis organisms increases resistance. In infection with rough, avirulent strains of S. iyphimurium the elimination of macro phages was not followed by an essential loss of resistance, and it appears that other non-specific defence mechanisms, for example the complement system, may have compensated for the lack of macrophages. Macrophages, therefore, play an important role in defence during primary infection with virulent strains. In immunity to challenge infection with S. typhimurium, macrophages play an even more significant role. Treatment with OS completely removes immunity, and both humoral and cell-mediated immune mechanisms seem to require the participation of macrophages.},
  language  = {en}
}