quote:
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LM:
The evolution of the bac flag would not have been completed in one fell swoop but by a step by step process.
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But there isn't any evidence of this.
Oh really? You should probably look before you post....here is a small subset of the evidence that you claim does not exist...
Microbiology. 2003 Nov;149(Pt 11):3051-72. Related Articles, Links
Type II protein secretion and its relationship to bacterial type IV pili and archaeal flagella.
Peabody CR, Chung YJ, Yen MR, Vidal-Ingigliardi D, Pugsley AP, Saier MH Jr.
Division of Biological Sciences, University of California at San Diego, La Jolla, CA 92093-0116, USA.
Homologues of the protein constituents of the Klebsiella pneumoniae (Klebsiella oxytoca) type II secreton (T2S), the Pseudomonas aeruginosa type IV pilus/fimbrium biogenesis machinery (T4P) and the Methanococcus voltae flagellum biogenesis machinery (Fla) have been identified. Known constituents of these systems include (1). a major prepilin (preflagellin), (2). several minor prepilins (preflagellins), (3). a prepilin (preflagellin) peptidase/methylase, (4). an ATPase, (5). a multispanning transmembrane (TM) protein, (6). an outer-membrane secretin (lacking in Fla) and (7). several functionally uncharacterized envelope proteins. Sequence and phylogenetic analyses led to the conclusion that, although many of the protein constituents are probably homologous, extensive sequence divergence during evolution clouds this homology so that a common ancestry can be established for all three types of systems for only two constituents, the ATPase and the TM protein. Sequence divergence of the individual T2S constituents has occurred at characteristic rates, apparently without shuffling of constituents between systems. The same is probably also true for the T4P and Fla systems. The family of ATPases is much larger than the family of TM proteins, and many ATPase homologues function in capacities unrelated to those considered here. Many phylogenetic clusters of the ATPases probably exhibit uniform function. Some of these have a corresponding TM protein homologue although others probably function without one. It is further shown that proteins that compose the different phylogenetic clusters in both the ATPase and the TM protein families exhibit unique structural characteristics that are of probable functional significance. The TM proteins are shown to have arisen by at least two dissimilar intragenic duplication events, one in the bacterial kingdom and one in the archaeal kingdom. The archaeal TM proteins are twice as large as the bacterial TM proteins, suggesting an oligomeric structure for the latter.
Publication Types:
Review
Review, Academic
Cell. 2004 May 14;117(4):527-39. Related Articles, Links
Decoding cilia function: defining specialized genes required for compartmentalized cilia biogenesis.
Avidor-Reiss T, Maer AM, Koundakjian E, Polyanovsky A, Keil T, Subramaniam S, Zuker CS.
Howard Hughes Medical Institute and Division of Biological Sciences and Department of Neurosciences, University of California at San Diego, La Jolla, CA 92093, USA.
The evolution of the ancestral eukaryotic flagellum is an example of a cellular organelle that became dispensable in some modern eukaryotes while remaining an essential motile and sensory apparatus in others. To help define the repertoire of specialized proteins needed for the formation and function of cilia, we used comparative genomics to analyze the genomes of organisms with prototypical cilia, modified cilia, or no cilia and identified approximately 200 genes that are absent in the genomes of nonciliated eukaryotes but are conserved in ciliated organisms. Importantly, over 80% of the known ancestral proteins involved in cilia function are included in this small collection. Using Drosophila as a model system, we then characterized a novel family of proteins (OSEGs: outer segment) essential for ciliogenesis. We show that osegs encode components of a specialized transport pathway unique to the cilia compartment and are related to prototypical intracellular transport proteins.
J Mol Microbiol Biotechnol. 2004;7(1-2):41-51. Related Articles, Links
Recent advances in the structure and assembly of the archaeal flagellum.
Bardy SL, Ng SY, Jarrell KF.
Department of Microbiology and Immunology, Queen's University, Kingston, Ont, Canada.
Archaeal motility occurs through the rotation of flagella that are distinct from the flagella found on bacteria. The differences between the two structures include the multi-flagellin nature of the archaeal filament, the widespread posttranslational modification of the flagellins and the presence of a short signal peptide on each flagellin that is cleaved by a specific signal peptidase prior to the incorporation of the mature flagellin into the flagellar filament. Research has revealed similarities between the archaeal flagellum and the type IV pilus, including the presence of similar unusual signal peptides on the flagellins and pilins, similarities in the amino acid sequences of the major structural proteins themselves, as well as similarities between potential assembly and processing components. The recent suggestion that type IV pili are part of a family of cell surface complexes, coupled with the similarities between type IV pili and archaeal flagella, raise questions about the evolution of these systems and possible inclusion of archaeal flagella into this surface complex family. Copyright 2004 S. Karger AG, Basel
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