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- Lundgren, Magnus, 1975-
(författare)
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Exploring the Cell Cycle of Archaea
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Archaea is the third domain of life, discovered only thirty years ago. In a microscope archaea appear indistinguishable from bacteria, but they have been shown to be more closely related to eukaryotes than to bacteria. Especially central information processing is homologous to that of eukaryotes. The archaea, previously thought to be limited to extreme environments, constitute a large part of life on Earth to an extent that has only begun to be understood. Despite their abundance little is known about several central cell-cycle features, such as cell division and genome segregation.For this thesis, a comprehensive study of the cell cycle in the model archaeon Sulfolobus acidocaldarius was performed, describing the majority of its cell-cycle regulated genes. Several known DNA replication genes, as well as genes previously not known to have a role in the cell cycle, displayed cyclic transcription. Several transcription factors, kinases and DNA sequence elements were identified as cell-cycle regulatory elements. Among the most important findings were putative cell division and genome segregation machineries.Sulfolobus species were discovered to have three origins of replication, constituting the first known prokaryotes with multiple origins. All origins initiate replication in a synchronous manner. Cdc6 proteins were shown to bind to origin recognition boxes conserved across the Archaea domain. Two Cdc6 proteins function as replication initiators, while a third paralog is implicated as a negative factor. Replication was shown to proceed at a rate similar to that of eukaryotes.A particular type of cell cycle organization was found to be unusually conserved in the Crenachaeota phylum. All the studied species displayed a short prereplicative phase and a long postreplicative phase, and cycle between one and two genome copies. Genome sizes were determined for several species. The euryarchaeon Methanothermobacter thermautotrophicus was also studied, and it was shown to initiate genome segregation during, or just after, replication. In contrast to the crenarchaea it never displayed a single genome copy per cell.
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| 2. |
- Pelve, Erik A., 1980-
(författare)
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Unique Solutions to Universal Problems : Studies of the Archaeal Cell
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Archaea is one of the three domains of life and studies of archaeal biology are important for understanding of life in extreme environments, fundamental biogeochemical processes, the origin of life, the eukaryotic cell and their own, unique biology. This thesis presents four studies of the archaeal cell, using the extremophilic Sulfolobus and ocean living Nitrosopumilus as model systems. Cell division in crenarchaea is shown to be carried out by a previously unknown system named Cdv (cell division). The system shares homology with the eukaryotic ESCRT-III system which is used for membrane reorganization during vesicle formation, viral release and cytokinesis. Organisms of the phylum Thaumarchaeota also use the Cdv system, despite also carrying genes for the euryarchaeal and bacterial cell division system FtsZ. The thaumarchaeal cell cycle is demonstrated to be dominated by the prereplicative and replicative stage, in contrasts to the crenarchaeal cell cycle where the cell at the majority of the time resides in the postreplicative stage. The replication rate is remarkably low and closer to what is measured for eukaryotes than other archaea. The gene organization of Sulfolobus is significantly associated with the three origins of replication. The surrounding regions are dense with genes of high importance for the organisms such as highly transcribed genes, genes with known function in fundamental cellular processes and conserved archaeal genes. The overall gene density is elevated and transposons are underrepresented. The archaeal virus SIRV2 displays a lytic life style where the host cell at the final stage of infection is disrupted for release of new virus particles. The remarkable pyramid-like structure VAP (virus associated pyramids), that is formed independently of the virus particle, is used for cell lysis. The research presented in this thesis describes unique features of the archaeal cell and influences our understanding of the entire tree of life.
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