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- Andersson, Jan O, et al.
(författare)
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Genome degradation is an ongoing process in Rickettsia
- 1999
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Ingår i: Molecular biology and evolution. - : SOC MOLECULAR BIOLOGY EVOLUTION. - 0737-4038 .- 1537-1719. ; 16:9, s. 1178-1191
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- To study reductive evolutionary processes in bacterial genomes, we examine sequences in the Rickettsia genomes which are unconstrained by selection and evolve as pseudogenes, one of which is the metK gene, which codes for AdoMet synthetase. Here, we sequenced the metK gene and three surrounding genes in eight different species of the genus Rickettsia. The metK gene was found to contain a high incidence of deletions in six lineages, while the three genes in its surroundings were functionally conserved in all eight lineages. A more drastic example of gene degradation was identified in the metK downstream region, which contained an open reading frame in Rickettsia felis. Remnants of this open reading frame could be reconstructed in five additional species by eliminating sites of frameshift mutations and termination codons. A detailed examination of the two reconstructed genes revealed that deletions strongly predominate over insertions and that there is a strong transition bias for point mutations which is coupled to an excess of GC-to-AT substitutions. Since the molecular evolution of these inactive genes should reflect the rates and patterns of neutral mutations, our results strongly suggest that there is a high spontaneous rate of deletions as well as a strong mutation bias toward AT pairs in the Rickettsia genomes. This may explain the low genomic G + C content (29%), the small genome size (1.1 Mb), and the high noncoding content (24%), as well as the presence of several pseudogenes in the Rickettsia prowazekii genome.
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- Andersson, Jan O, et al.
(författare)
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Genomic rearrangements during evolution of the obligate intracellular parasite Rickettsia prowazekii as inferred from an analysis of 52015 bp nucleotide sequence
- 1997
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Ingår i: Microbiology. - 1350-0872 .- 1465-2080. ; 143:8, s. 2783-2795
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In this study a description is given of the sequence and analysis of 52 kb from the 1.1 Mb genome of Rickettsia prowazekii, a member of the alpha-Proteobacteria. An investigation was made of nucleotide frequencies and amino acid composition patterns of 41 coding sequences, distributed in 10 genomic contigs, of which 32 were found to have putative homologues in the public databases. Overall, the coding content of the individual contigs ranged from 59 to 97%, with a mean of 81%. The genes putatively identified included genes involved in the biosynthesis of nucleotides, macromolecules and cell wall structures as well as citric acid cycle component genes. In addition, a putative identification was made of a member of the regulatory response family of two-component signal transduction systems as well as a gene encoding haemolysin. For one gene, the homologue of metK, an internal stop codon was discovered within a region that is otherwise highly conserved. Comparisons with the genomic structures of Escherichia coli, Haemophilus influenzae and Bacillus subtilis have revealed several atypical gene organization patterns in the R. prowazekii genome. For example, R. prowazekii was found to have a unique arrangement of genes upstream of dnaA in a region that is highly conserved among other microbial genomes and thought to represent the origin of replication of a primordial replicon. The results presented in this paper support the hypothesis that the R. prowazekii genome is a highly derived genome and provide examples of gene order structures that are unique for the Rickettsia.
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- Andersson, Jan O, et al.
(författare)
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Insights into the evolutionary process of genome degradation
- 1999
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Ingår i: Current Opinion in Genetics and Development. - 0959-437X .- 1879-0380. ; 9:6, s. 664-671
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Tidskriftsartikel (refereegranskat)abstract
- Studies of noncoding and pseudogene sequence diversity, particularly in Rickettsia, have begun to reveal the basic principles of genome degradation in microorganisms. Increasingly, studies of genes and genomes suggest that there has been an extensive amount of horizontal gene transfer among microorganisms. As this inflow of genetic material does not seem generally to have resulted in genome size expansions, however, degenerative processes must be at the very least as widespread as horizontal gene transfer. The basic principles of gene degradation and elimination that are being explored in Rickettsia are likely to be of major importance for our understanding of how microbial genomes evolve.
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- Andersson, Lars Gustaf, et al.
(författare)
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De kulturella förändringarna
- 1999
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Ingår i: Skolan och de kulturella förändringarna. - 9144007930
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Discussion concerning school and cultural change
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- Andersson, Lars Gustaf, et al.
(författare)
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Kulturell identitet
- 1999
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Ingår i: Skolan och de kulturella förändringarna. - 9144007930
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Discussion concerning the concept of cultural identity in connection with education and media pedagogy
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- Andersson, Lars Gustaf, et al.
(författare)
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Mediekritik och mediepedagogik
- 1999
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Ingår i: Skolan och de kulturella förändringarna. - 9144007930
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Discussion concerning media criticism and media pedagogy in modern education
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- Andersson, Lars Gustaf, et al.
(författare)
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Pedagogikens mysterier
- 1997
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Ingår i: Italienska förbindelser. - 918839610X
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Bokkapitel (populärvet., debatt m.m.)abstract
- Survey over the theme of pedagogy in the works of Pier Paolo Pasolini, Andrea Zanzotto and Alberto Moravia
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