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NASA NTRS1987

A possible biochemical missing link among archaebacteria

The characteristics of the newly discovered strain of archaebacteria, VC-16, the only archaebacterium known to reduce sulfate, suggest that VC-16 might represent a transitional form between an anaerobic thermophilic sulfur-based type of metabolism and methanogenesis. It is shown here, using a matrix of evolutionary distances derived from an alignment of various archaebacterial 16S rRNAs and the phylogenetic tree derived from these evolutionary distances, that the lineage represented by strain VC-16 arises from the archaebacterial tree precisely where such an interpretation would predict that it would, between the Methanococcus lineage and that of Thermococcus.

Achenbach-Richter, Laurie↗

NASA NTRS1998

The prokaryote-to-eukaryote transition reflected in the evolution of the V/F/A-ATPase catalytic and proteolipid subunits

Changes in the primary and quarternary structure of vacuolar and archaeal type ATPases that accompany the prokaryote-to-eukaryote transition are analyzed. The gene encoding the vacuolar-type proteolipid of the V-ATPase from Giardia lamblia is reported. Giardia has a typical vacuolar ATPase as observed from the common motifs shared between its proteolipid subunit and other eukaryotic vacuolar ATPases, suggesting that the former enzyme works as a hydrolase in this primitive eukaryote. The phylogenetic analyses of the V-ATPase catalytic subunit and the front and back halves of the proteolipid subunit placed Giardia as the deepest branch within the eukaryotes. Our phylogenetic analysis indicated that at least two independent duplication and fusion events gave rise to the larger proteolipid type found in eukaryotes and in Methanococcus. The spatial distribution of the conserved residues among the vacuolar-type proteolipids suggest a zipper-type interaction among the transmembrane helices and surrounding subunits of the V-ATPase complex. Important residues involved in the function of the F-ATP synthase proteolipid have been replaced during evolution in the V-proteolipid, but in some cases retained in the archaeal A-ATPase. Their possible implication in the evolution of V/F/A-ATPases is discussed.

NASA Discipline Exobiology↗

NASA NTRS1997

Conserved gene clusters in bacterial genomes provide further support for the primacy of RNA

Five complete bacterial genome sequences have been released to the scientific community. These include four (eu)Bacteria, Haemophilus influenzae, Mycoplasma genitalium, M. pneumoniae, and Synechocystis PCC 6803, as well as one Archaeon, Methanococcus jannaschii. Features of organization shared by these genomes are likely to have arisen very early in the history of the bacteria and thus can be expected to provide further insight into the nature of early ancestors. Results of a genome comparison of these five organisms confirm earlier observations that gene order is remarkably unpreserved. There are, nevertheless, at least 16 clusters of two or more genes whose order remains the same among the four (eu)Bacteria and these are presumed to reflect conserved elements of coordinated gene expression that require gene proximity. Eight of these gene orders are essentially conserved in the Archaea as well. Many of these clusters are known to be regulated by RNA-level mechanisms in Escherichia coli, which supports the earlier suggestion that this type of regulation of gene expression may have arisen very early. We conclude that although the last common ancestor may have had a DNA genome, it likely was preceded by progenotes with an RNA genome.

Non-NASA Center↗