MFPL - 2014 RESEARCH GROUPS
ANGELA WITTE
φCh1, a model for gene regulation in haloalkaliphilic archaea The virus φCh1 was found by spontaneous lysis of a culture of the haloalkaliphilic archaeon, Natrialba magadii, an isolate from the soda lake, Lake Magadii in Kenya.
Angela Witte TEAM
Tina Grohmann Christoph Hofbauer Agnes Kogler Kathrin Schönfelder
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This organism has an optimal growth at 3.5M NaCl and at a pH of 9.5. The virus itself is used as a model system to analyze gene expression in haloalkaliphilic organisms, facing with two extremes: a high pH and high concentrations of salt. The sequence of φCh1, infecting the haloalkaliphilic archaeon Natrialba magadii, contains an open reading frame (int1) in the central part of its genome that belongs to the λ integrase family of site-specific recombinases. Sequence similarities to known integrases include the highly conserved tetrad R-H-R-Y. The flanking sequences of int1 contain several direct repeats of 30 bp in length (IR-L and IR-R), which are orientated in an inverted direction. The invertible region encodes two structural proteins (gp34 and gp36, encoded by ORF34 and ORF36) expected to represent the viral tail fibre proteins. In vitro experiments using purified protein variants gp341 and gp3452 (containing the C-terminus of gp36) revealed exclusive binding of gp3452 but not of gp341 to cells of the cured strain Nab. magadii L13. This specific binding could be inhibited by the addition of α-D-galactose. α-D-galactose also significantly reduced the infectivity of φCh1. Binding experiments employing distinct domains of gp341 and gp3452 indicated the C-terminus to be responsible for binding to the receptor on the cell surface of Nab. magadii L13. This C-terminus contains a domain with similarities to the super-family of “galactose-like binding” proteins. In summary, the experiments gave evidence that gp3452 represents the anti-receptor of φCh1 that binds to specific carbohydrate ligands located on the cell surface of Nab. magadii. Currently the work concentrates on the identification and function of repressor and activator molecules encoded by the virus, gene regulation
due to a recombination event, identification of the receptor for the virus on the cell surface of Nab. magadii and the transformation/shuttle vector system developed by the group. In addition, the method is used to construct different mutants.
Electron micrograph of φCh1 particle negatively stained with uranylacetate.
SELECTED PUBLICATIONS Mayrhofer-Iro M, Ladurner A, Meissner C, Derntl C.,Reiter M, Haider F, Dimmel, K. Rössler N, Klein R, Baranyi U, Scholz H, Witte A. Utilization of virus φCh1 elements to establish a shuttle vector system for halo(alkali)philic Archaea via transformation of Natrialba magadii. Appl Environ Microbial. 2013;79(8):2741-2748. PMID: 23416999 Klein R, Rössler N, Iro M, Scholz H, Witte A. Haloarchaeal myovirus φCh1 harbours a phase variation system for the production of protein variants with distinct cell surface adhesion specificities. Mol Microbiol. 2012;83(1):137-50. PMID: 22111759 Iro M, Klein R, Gálos B, Baranyi U, Rössler N, Witte A. The lysogenic region of virus phiCh1: identification of a repressor-operator system and determination of its activity in halophilic Archaea. Extremophiles. 2007;11(2):383-96. PMID: 17123129