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  • 1
    ISSN: 1432-0983
    Keywords: Cryptomonads (Pyrenomonas salina) ; Plastid DNA ; SSUrRNA sequence ; Plastid evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cryptomonads are thought to have arisen from a symbiotic association between a eukaryotic flagellated host and a eukaryotic algal symbiont, presumably related to red algae. As organellar DNAs have proven to be useful tools in elucidating phylogenetic relationships, the plastid (pt) DNA of the cryptomonad alga Pyrenomonas salina has been characterized in some detail. A restriction map of the circular 127 kb ptDNA from Pyrenomonas salina was established. An inverted repeat (IR) region of about 5 kb separates two single-copy regions of 15 and 102 kb, respectively. It contains the genes for the small and large subunit of rRNA. Ten protein genes, coding for the large subunit of ribulose-1,5-bisphosphate carboxylase, the 47 kDa, 43 kDa and 32 kDa proteins of photosystem II, the ribosomal proteins L2, S7 and S11, the elongation factor Tu, as well as the α- and β-subunits of ATP synthase, have been localized on the restriction map either by hybridization of heterologous gene probes or by sequence homologies. The gene for the plastidal small subunit (SSUr) RNA has been sequenced and compared to homologous SSU regions from the cyanobacterium Anacystis nidulans and plastids from rhodophytes, chromophytes, euglenoids, chlorophytes, and land plants. A phylogenetic tree constructed with the neighborliness method and indicating a relationship of cryptomonad plastids with those of red algae is presented.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1617-4623
    Keywords: Cryptomonads ; Nucleomorph ; Small subunit ribosomal RNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In cryptomonads, unicellular phototrophic flagellates, the plastid(s) is (are) located in a special narrow compartment which is bordered by two membranes; it harbours neither mitochondria nor Golgi dictyosomes but comprises eukaryotic ribosomes and starch grains together with a small organelle called the nucleomorph. The nucleomorph contains DNA and is surrounded by a double membrane with pores. It is thought to be the vestigial nucleus of a phototrophic eukaryotic endosymbiont. Cryptomonads are therefore supposed to represent an intermediate state in the evolution of complex plastids from endosymbionts. We have succeeded in isolating pure nucleomorph fractions, and can thus provide, using pulsed field gel electrophoresis, polymerase chain reaction and sequence analysis, definitive proof for the eukaryotic nature of the symbiont and its phylogenetic origin.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Naturwissenschaften 83 (1996), S. 103-112 
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Notes: 9 years. During most of this time, evolution took place at the level of cell evolution. The cells of presently existing organisms belong to two fundamentally different cell types, protocytes (of bacteria and archaea) and eucytes (of eukarya). Thanks to molecular phylogenetics, the path of evolution can now be traced back to its very beginnings, although the picture may be blurred by repeated horizontal gene transfer. A symbiogenetic origin of plastids and mitochondria is now very well documented, and it is being discussed also for some other constituents of eucytes, including even the cell nucleus. It could be demonstrated that not only did bacterial cells become incorporated into protoeucytes and transformed into organelles of their respective hosts, but also that endocytic eucytes have apparently been transformed to complex organelles by coevolution with host cells.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Naturwissenschaften 83 (1996), S. 103-112 
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
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