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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

A comment on methanogenic bacteria and the primitive ecology

As the phenotype of methanogenic bacteria is suggested to have been one of the major factors creating a dynamic balance between CO2 and CH4 in the primitive atmosphere, these organisms are thought to be very ancient. Their antiquity may be further postulated by comparative characterization of their ribosomal RNA. Accepting this antiquity, it is concluded that a carbon-dioxide-methane cycle, driven by photosynthesis, was the major carbon cycle in primitive ecology, and that photosynthesis and methanogens were thus contemporaneous.

Woese, C. R.↗
NASA NTRS1978

Origins of prokaryotes, eukaryotes, mitochondria, and chloroplasts

A computer branching model is used to analyze cellular evolution. Attention is given to certain key amino acids and nucleotide residues (ferredoxin, 5s ribosomal RNA, and c-type cytochromes) because of their commonality over a wide variety of cell types. Each amino acid or nucleotide residue is a sequence in an inherited biological trait; and the branching method is employed to align sequences so that changes reflect substitution of one residue for another. Based on the computer analysis, the symbiotic theory of cellular evolution is considered the most probable. This theory holds that organelles, e.g., mitochondria and chloroplasts invaded larger bodies, e.g., bacteria, and combined functions to form eucaryotic cells.

Schwartz, R. M.↗
NASA NTRS1978

Evolution of early life inferred from protein and ribonucleic acid sequences

The chemical structures of ferredoxin, 5S ribosomal RNA, and c-type cytochrome sequences have been employed to construct a phylogenetic tree which connects all major photosynthesizing organisms: the three types of bacteria, blue-green algae, and chloroplasts. Anaerobic and aerobic bacteria, eukaryotic cytoplasmic components and mitochondria are also included in the phylogenetic tree. Anaerobic nonphotosynthesizing bacteria similar to Clostridium were the earliest organisms, arising more than 3.2 billion years ago. Bacterial photosynthesis evolved nearly 3.0 billion years ago, while oxygen-evolving photosynthesis, originating in the blue-green algal line, came into being about 2.0 billion years ago. The phylogenetic tree supports the symbiotic theory of the origin of eukaryotes.

Dayhoff, M. O.↗
NASA NTRS1980

Physical chemistry and evolution of salt tolerance in halobacteria

The cellular constituents of extremely halophilic bacteria not only tolerate high salt concentration, but in many cases require it for optical functioning. The characteristics affected by salt include enzyme activity, stability, allosteric regulation, conformation and subunit association. The salt effects are of two major kinds: electrostatic shielding of negative charges by cations at low salt concentration, and hydrophobic stabilization by salting-out type salts at high salt concentration. The composition of halobacterial proteins shows an excess of acidic amino acids and a deficiency of nonpolar amino acids, which accounts for these effects. Since the cohesive forces are weaker and the repulsing forces are stronger in these proteins, preventing aggregation in salt, these structures are no longer suited for functioning in the absence of high salt concentrations. Unlike these nonspecific effects, ribosomes in halobacteria show marked preference for potassium over sodium ions. To ensure the proper intracellular ionic composition, powerful ion transport systems have evolved in the halobacteria, resulting in the extrusion of sodium ions and their replacement by potassium. It is likely that such membrane transport system for ionic movements is a necessary requisite for salt tolerance.

Lanyi, J. K.↗
NASA NTRS1981

The nucleotide sequence of Beneckea harveyi 5S rRNA

The primary sequence of the 5S ribosomal RNA isolated from the free-living bioluminescent marine bacterium Beneckea harveyi is reported and discussed in regard to indications of phylogenetic relationships with the bacteria Escherichia coli and Photobacterium phosphoreum. Sequences were determined for oligonucleotide products generated by digestion with ribonuclease T1, pancreatic ribonuclease and ribonuclease T2. The presence of heterogeneity is indicated for two sites. The B. harveyi sequence can be arranged into the same four helix secondary structures as E. coli and other prokaryotic 5S rRNAs. Examination of the 5S-RNS sequences of the three bacteria indicates that B. harveyi and P. phosphoreum are specifically related and share a common ancestor which diverged from an ancestor of E. coli at a somewhat earlier time, consistent with previous studies.

Luehrsen, K. R.↗
NASA NTRS1981

Phylogenetic sequence of metabolic pathways in Precambrian cellular life

A sequence of major metabolic events is presented as they may have appeared during prokaryote evolution. This is based on (1) the phylogenetic schema derived from sequences of bacterial ferredoxin, 2Fe-2S ferredoxin, 5S ribosomal RNA, and c-type cytochromes; (2) metabolic settings in which these macromolecules are found; and (3) metabolic capabilities of the prokaryotes that carry these molecules.

Barnabas, J.↗
NASA NTRS1981

Evolution of the rhodospirillaceae and mitochondria - A view based on sequence data

New sequence data from several protein families and from 5S ribosomal RNA confirm and elaborate a previously proposed description of the phylogenetic connections between a variety of bacteria and the eukaryotes. Probably, the first organisms were nonphotosynthetic anaerobic prokaryotes, which were followed soon by photosynthetic anaerobes. From this photosynthetic stock, the aerobic line to Pseudomonadacae, Rhodospirillaceae, and blue-greens arose. The eukaryotes derived genetic material from the symbioses of at least three separate bacterial lines. Ancestors of Rhodopseudomonas globiformis gave rise to the eukaryote mitochondria, probably through at least three separate symbioses, one early on the flagellate line, one on the ciliate line, and one on the stem to the multicellular forms.

Dayhoff, M. O.↗
NASA NTRS1982

Evolution of major metabolic innovations in the Precambrian

A combination of information on the metabolic capabilities of prokaryotes with a composite phylogenetic tree depicting an overview of prokaryote evolution based on the sequences of bacterial ferredoxin, 2Fe-2S ferredoxin, 5S ribosomal RNA, and c-type cytochromes shows three zones of major metabolic innovation in the Precambrian. The middle of these, which reflects the genesis of oxygen-releasing photosynthesis and aerobic respiration, links metabolic innovations of the anaerobic stem on the one hand and, on the other, proliferation of aerobic bacteria and the symbiotic associations leading to the eukaryotes. Those pathways where information on the structure of the enzymes is known are especially considered. Halobacterium and Thermoplasma (archaebacteria) do not belong to a totally independent line on the basis of the composite tree but branch from the eukaryote cytoplasmic line.

Barnabas, J.↗
NASA NTRS1984

Evolution of prokaryote and eukaryote lines inferred from sequence evidence

This paper describes the evolution of prokaryotes and early eukaryotes, including their symbiotic relationships, as inferred from phylogenetic trees of bacterial ferredoxin, 5S ribosomal RNA, ribulose-1,5-biphosphate carboxylase large chain, and mitochondrial cytochrome oxidase polypeptide II.

Hunt, L. T.↗
NASA NTRS1983

Sequence evidence for the symbiotic origins of chloroplasts and mitochondria

The origin of mitochondria and chloroplasts is investigated on the basis of prokaryotic and early-eukaryotic evolutionary trees derived from protein and nucleic-acid sequences by the method of Dayhoff (1979). Trees for bacterial ferrodoxins, 5S ribosomal RNA, c-type cytochromes, the lipid-binding subunit of ATPase, and dihydrofolate reductase are presented and discussed. Good agreement among the trees is found, and it is argued that the mitochondria and chloroplasts evolved by multiple symbiotic events.

George, D. G.↗
NASA NTRS1985

Insights into the phylogenetic positions of photosynthetic bacteria obtained from 5S rRNA and 16S rRNA sequence data

Comparisons of complete 16S ribosomal ribonucleic acid (rRNA) sequences established that the secondary structure of these molecules is highly conserved. Earlier work with 5S rRNA secondary structure revealed that when structural conservation exists the alignment of sequences is straightforward. The constancy of structure implies minimal functional change. Under these conditions a uniform evolutionary rate can be expected so that conditions are favorable for phylogenetic tree construction.

Fox, G. E.↗
NASA NTRS1984

Cell symbiosis theory - Status and implications for the fossil record

Smith (1981) has presented three alternative models of the origin of eukaryotes. In the present investigation, alternative theories are discussed along with the status of serial endosymbiotic theory. It is pointed out that the usefulness of the serial endosymbiotic theory is attested by the great flourishing of productive scientific studies it has generated. Attention is given to the origin of mitochondria and plastids from free-living bacteria, the polyphyly of mitochondria, the origin of the nuclear membrane, the origin of undulipodia (cilia and other 9 + 2 organelles), the sequence of acquisition of organelles, large ribosomes, genome organization, animals and plants, and systematics and axonomy of the microorganisms.

Margulis, L.↗
NASA NTRS1986

A comparative study of prebiotic and present day translational models

It is generally recognized that the understanding of the molecular basis of primitive translation is a fundamental step in developing a theory of the origin of life. However, even in modern molecular biology, the mechanism for the decoding of messenger RNA triplet codons into an amino acid sequence of a protein on the ribosome is understood incompletely. Most of the proposed models for prebiotic translation lack, not only experimental support, but also a careful theoretical scrutiny of their compatibility with well understood stereochemical and energetic principles of nucleic acid structure, molecular recognition principles, and the chemistry of peptide bond formation. Present studies are concerned with comparative structural modelling and mechanistic simulation of the decoding apparatus ranging from those proposed for prebiotic conditions to the ones involved in modern biology. Any primitive decoding machinery based on nucleic acids and proteins, and most likely the modern day system, has to satisfy certain geometrical constraints. The charged amino acyl and the peptidyl termini of successive adaptors have to be adjacent in space in order to satisfy the stereochemical requirements for amide bond formation. Simultaneously, the same adaptors have to recognize successive codons on the messenger. This translational complex has to be realized by components that obey nucleic acid conformational principles, stabilities, and specificities. This generalized condition greatly restricts the number of acceptable adaptor structures.

Rein, R.↗
NASA NTRS1989

Phylogenetic perspective and the search for life on earth and elsewhere

Any search for microbial life on Mars cannot rely upon cultivation of indigenous organisms. Only a minority of even terrestrial organisms that are observed in mixed, naturally-occurring microbial populations can be cultivated in the laboratory. Consequently, methods are being developed for analyzing the phylogenetic affiliations of the constituents of natural microbial populations without the need for their cultivation. This is more than an exercise in taxonomy, for the extent of phylogenetic relatedness between unknown and known organisms is some measure of the extent of their biochemical commonalities. In one approach, total DNA is isolated from natural microbial populations and 16S rRNA genes are shotgun cloned for rapid sequence determinations and phylogenetic analyses. A second approach employs oligodeoxynucleotide hybridization probes that bind to phylogenetic group-specific sequences in 16S rRNA. Since each actively growing cell contains about 104 ribosomes, the binding of the diagnostic probes to single cells can be visualized by radioactivity or fluorescence. The application of these methods and the use of in situ cultivation techniques is illustrated using submarine hydrothermal vent communities. Recommendations are made regarding planning toward future Mars missions.

Pace, Norman R.↗
NASA NTRS1991

Exploration of RNA structure spaces

In order to understand the structure of real structure spaces, we are studying the 5S rRNA structure space experimentally. A plasmid containing a synthetic 5S rRNA gene, two rRNA promoters, and transcription terminators has been assembled. Assays are conducted to determine if the foreign 5S rRNA is expressed, and to see whether or not it is incorporated into ribosomes. Evolutionary competition is used to determine the relative fitness of strains containing the foreign 5S rRNA and a control 5S rRNA. By using site directed mutagenesis, a number of mutants can be made in order to study the boundaries of the structure space and how sharply defined they are. By making similar studies in the vicinity of structure space, it will be possible to determine how homogeneous the 5S rRNA structure space is. Useable experimental protocols have been developed, and a number of mutants have already been studied. Initial results suggest an explanation of why single stranded regions of the RNA are less subject to mutation than double stranded regions.

Fox, G. E.↗
NASA NTRS1992

The origin and early evolution of nucleic acid polymerases

The hypothesis that vestiges of the ancestral RNA-dependent RNA polymerase involved in the replication of RNA genomes of Archean cells are present in the eubacterial RNA-polymerase beta-prime subunit and its homologues is discussed. It is shown that, in the DNA-dependent RNA polymerases from three cellular lineages, a very conserved sequence of eight amino acids, also found in a small RNA-binding site previously described for the E. coli polynucleotide phosphorylase and the S1 ribosomal protein, is present. The optimal conditions for the replicase activity of the avian-myeloblastosis-virus reverse transcriptase are presented. The evolutionary significance of the in vitro modifications of substrate and template specificities of RNA polymerases and reverse transcriptases is discussed.

Lazcano, A.↗
NASA NTRS1993

The RNA-world and co-evolution hypothesis and the origin of life: Implications, research strategies and perspectives

The applicability of the RNA-world and co-evolution hypothesis to the study of the very first stages of the origin of life is discussed. The discussion focuses on the basic differences between the two hypotheses and their implications, with regard to the reconstruction methodology, ribosome emergence, balance between ribozymes and protein enzymes, and their major difficultites. Additional complexities of the two hypotheses, such as membranes and the energy source of the first reactions, are not treated in the present work. A central element in the proposed experimental strategies is the study of the catalytic activites of very small peptides and RNA-like oligomers, according to existing, as well as to yet-to-be-invented scenarios of the two hypothesis under consideration. It is suggested that the novel directed molecular evolution technology, and molecular computational modeling, can be applied to this research. This strategy is assumed to be essential for the suggested goal of future studies of the origin of life, namely, the establishment of a `Primordial Darwinian entity'.

Lahav, Noam↗
NASA NTRS1994

Experiment K-7-18: Effects of Spaceflight in the Muscle Adductor Longus of Rats Flown in the Soviet Biosatellite Cosmos 2044: A Study Employing Neural Cell Adhesion Molecules (N-CAM) Immunocytochemistry and Conventional Morphological Techniques (Light and Electron Microscopy) - Part 1

The effects of spaceflight upon the 'slow' muscle adductor longus was examined in rats flown in the Soviet Biosatellite COSMOS 2044. Three groups - synchronous, vivarium and basal served as controls. The techniques employed included standard methods for light microscopy, N-CAM immunocytochemistry and electron microscopy. Light microscopic observations revealed myofiber atrophy, contraction bands and segmental necrosis accompanied by cellular infiltrates composed of macrophages, leucocytes and mononuclear cells. N-CAM immunoreactivity was seen (N-CAM-IR) on the myofiber surface, satellite cells and in regenerating myofibers reminiscent of myotubes. Ultrastructural alterations included Z band streaming, disorganization of myofibrillar architecture, sarcoplasmic degradation, extensive segmental necrosis with preservation of the basement membrane, degenerative phenomena of the capillary endothelium and cellular invasion of necrotic areas. Regenerating myofibers were identified by the presence of increased amounts of ribosomal aggregates and chains of polyribosomes associated with myofilaments that displayed varied distributive patterns. The principal electron microscopic changes of the neuromuscular junctions consisted of a decrease or absence of synaptic vesicles, degeneration of axon terminals, increased number of microtubules, vacant axonal spaces and axonal sprouting. The present observations indicate that major alterations such as myofibrillar disruption and necrosis, muscle regeneration and denervation and synaptic remodeling at the level of the neuromuscular junction may take place during spaceflight.

Daunton, N. G.↗