RESUMO
An analysis of the small subunit ribosomal RNA (16S-like rRNA) from the protozoan Giardia lamblia provided a new perspective on the evolution of nucleated cells. Evolutionary distances estimated from sequence comparisons between the 16S-like rRNAs of Giardia lamblia and other eukaryotes exceed similar estimates of evolutionary diversity between archaebacteria and eubacteria and challenge the phylogenetic significance of multiple eukaryotic kingdoms. The Giardia lamblia 16S-like rRNA has retained many of the features that may have been present in the common ancestor of eukaryotes and prokaryotes.
Assuntos
Giardia/genética , Filogenia , RNA Ribossômico/genética , Animais , Sequência de Bases , Humanos , Dados de Sequência Molecular , Conformação de Ácido Nucleico , RNA Ribossômico 16S/genéticaRESUMO
Polymerase chain reaction conditions were established for the in vitro amplification of eukaryotic small subunit ribosomal (16S-like) rRNA genes. Coding regions from algae, fungi, and protozoa were amplified from nanogram quantities of genomic DNA or recombinant plasmids containing rDNA genes. Oligodeoxynucleotides that are complementary to conserved regions at the 5' and 3' termini of eukaryotic 16S-like rRNAs were used to prime DNA synthesis in repetitive cycles of denaturation, reannealing, and DNA synthesis. The fidelity of synthesis for the amplification products was evaluated by comparisons with sequences of previously reported rRNA genes or with primer extension analyses of rRNAs. Fewer than one error per 2000 positions were observed in the amplified rRNA coding region sequences. The primary structure of the 16S-like rRNA from the marine diatom, Skeletonema costatum, was inferred from the sequence of its in vitro amplified coding region.
Assuntos
Amplificação de Genes , RNA Ribossômico/genética , Sequência de Bases , Clonagem Molecular , Dados de Sequência Molecular , FilogeniaRESUMO
We have determined the complete sequence of two structurally distinct 18S ribosomal RNA genes from the malarial parasite Plasmodium falciparum. S1 nuclease analyses demonstrate that only one of the genes is represented in stable rRNA populations isolated from blood-stage parasites. Comparisons of homologous rRNA genes from Plasmodium berghei and P. falciparum reveal that they are identical at 86% of their positions. From comparisons of the Plasmodium genes to that of humans, it was possible to design genus-specific as well as species-specific oligonucleotide probes that can be used to distinguish the parasite 18S ribosomal RNA from that of its host. The utilization of these probes as diagnostic reagents is discussed.
Assuntos
Genes , Plasmodium falciparum/genética , RNA Ribossômico 18S/genética , RNA Ribossômico/genética , Animais , Sequência de Bases , Endonucleases , Humanos , Dados de Sequência Molecular , Hibridização de Ácido Nucleico , Oligonucleotídeos/genética , Plasmídeos , Plasmodium berghei/genética , Endonucleases Específicas para DNA e RNA de Cadeia Simples , Especificidade da Espécie , Transcrição GênicaRESUMO
We have sequenced the coding region for the small-subunit rRNA gene from Paramecium tetraurelia. Similarity comparisons between small-subunit rRNAs from representatives of the Metazoa, the Plantae, the Fungi and four other members of the Ciliophora were used to construct phylogenetic trees. In these phylogenies the Ciliophora diverged from the eukaryotic line of descent as a loose phylogenetic grouping during a radiative period that gave rise to the Fungi, the Plantae and the Metazoa.
Assuntos
Cilióforos/genética , Paramecium/genética , RNA Ribossômico/genética , Animais , Sequência de Bases , Computadores , Dictyostelium/genética , Escherichia coli/genética , Halobacterium/genética , Filogenia , Ratos/genética , Xenopus laevis/genética , Zea mays/genéticaRESUMO
The small subunit ribosomal RNA (16S-like rRNA) coding regions of the hypotrichous ciliates Onychodromus quadricornutus and Oxytricha granulifera were amplified using polymerase chain reaction techniques. Complete sequences were determined for the amplified genes and compared to those of other ciliated protozoa. In phylogenetic trees inferred using distance matrix methods oxytrichids are not seen as a cohesive phylogenetic group. Oxytricha nova is most closely related to Stylonychia pustulata in a lineage that also includes O. quadricornutus. This phylogeny contradicts phylogenetic schemes in which Onychodromus is considered to be a primitive hypotrichous ciliate and suggests that O. nova was misidentified as members of the genus Oxytricha.
Assuntos
Evolução Biológica , Cilióforos/genética , RNA Ribossômico 16S/química , Animais , Sequência de Bases , Dados de Sequência Molecular , Filogenia , Reação em Cadeia da PolimeraseRESUMO
We have determined the complete nucleotide sequence of the small-subunit ribosomal RNA genes for the ciliate protozoans Stylonychia pustulata and Oxytricha nova. The sequences are homologous and sufficiently similar that these organisms must be closely related. In a phylogeny inferred from comparisons of several eukaryotic small-subunit ribosomal RNAs, the divergence of the ciliates from the eukaryotic line of descent is seen to coincide with the radiation of the plants, the animals, and the fungi. This radiation is preceded by the divergence of the slime mold, Dictyostelium discoideum.
Assuntos
Cilióforos/genética , RNA Ribossômico/genética , Animais , Sequência de Bases , Dados de Sequência Molecular , Filogenia , Homologia de Sequência do Ácido Nucleico , Especificidade da EspécieRESUMO
The small-subunit rRNA gene sequences of the flagellated protists Euglena gracilis and Trypanosoma brucei were determined and compared to those of other eukaryotes. A phylogenetic tree was constructed in which the earliest branching among the eukaryotes is represented by E. gracilis. The E. gracilis divergence far antedates a period of massive evolutionary radiation that gave rise to the plants, animals, fungi, and certain groups of protists such as ciliates and the acanthamoebae. The genetic diversity in this collection of eukaryotes is seen to exceed that displayed within either the eubacterial or the archaebacterial lines of descent.
Assuntos
Evolução Biológica , DNA Ribossômico , Euglena/genética , RNA Ribossômico , Trypanosoma brucei brucei/genética , Animais , Sequência de Bases , Clonagem Molecular , Dictyostelium/genética , Genes , RNA Bacteriano/genética , Homologia de Sequência do Ácido NucleicoRESUMO
We have determined the complete nucleotide sequence of the coding region of the small subunit rRNA gene of the hypotrichous ciliate Euplotes aediculatus. It is 1882 nucleotides long and contains several inserts not present in the small subunit rRNA genes of the hypotrichs Oxytricha nova and Stylonychia pustulata. A comparison of the sequences suggests that E. aediculatus is much less closely related to these other two hypotrichs than they are to each other. Although the gene sequence of E. aediculatus is drifting more rapidly than those of these other two species, its faster evolutionary clock is not enough to account for the degree of difference between them.
Assuntos
Cilióforos/genética , Genes , RNA Ribossômico/genética , Animais , Sequência de Bases , Clonagem Molecular , Enzimas de Restrição do DNA , Escherichia coli/genética , Plasmídeos , Saccharomyces cerevisiae/genética , Homologia de Sequência do Ácido Nucleico , Especificidade da EspécieRESUMO
Pneumocystis carinii pneumonia is the most common opportunistic infection in AIDS, and accounts for significant morbidity and mortality in these and other immunocompromised patients. P. carinii is a eukaryotic microorganism of uncertain taxonomy that can infect numerous mammalian hosts. Developing from a small, unicellular 'trophozoite' into a 'cyst' containing eight 'sporozoites', its life cycle superficially resembles those seen both in the Protozoa and Fungi. Morphological and ultrastructural observations have lead some investigators to conclude that the organism is a protozoan, while others have felt that it more closely resembles a fungus. Phylogenetic relationships can be inferred from comparisons of macromolecular sequences. Small subunit ribosomal RNAs (16S-like rRNAs) are well-suited for this purpose because they have the same function in all organisms and contain sufficient information to estimate both close and distant evolutionary relationships. Phylogenetic frameworks based upon such comparisons reveal that the plant, animal and fungal lineages are distinct from the diverse spectrum of protozoan lineages. In this letter, phylogenetic analysis of Pneumocystis 16S-like rRNA demonstrates it to be a member of the Fungi.