|
|
|
|
|
|
The Caulobacter crescentus CgtAC Protein Cosediments with the Free 50S Ribosomal Subunit. Bin Lin, 2004.The Obg family of GTPases is widely conserved and predicted to play an as-yet-unknown role in translation . Recent reports provide circumstantial evidence that both eukaryotic and prokaryotic Obg proteins are associated with the large ribosomal subunit . Here we provide direct evidence that the Caulobacter crescentus CgtAC protein is associated with the free large (50S) ribosomal subunit but not with 70S monosomes or with translating ribosomes . In contrast to the Bacillus subtilis and Escherichia coli proteins, CgtAC does not fractionate in a large complex by gel filtration, indicating a moderately weak association with the 50S subunit . Moreover, binding of CgtAC to the 50S particle is sensitive to salt concentration and buffer composition but not guanine nucleotide occupancy of CgtAC . Assays of epitope-tagged wild-type and mutant variants of CgtAC indicate that the C terminus of CgtAC is critical for 50S association . Interestingly, the addition of a C-terminal epitope tag also affected the ability of various cgtAC alleles to function in vivo . Depletion of CgtAC led to perturbations in the polysome profile, raising the possibility that CgtAC is involved in ribosome assembly or stability . Biochemical Characterization of a Mutationally Altered Protein Translocase: Proton Motive Force Stimulation of the Initiation Phase of Translocation. Hiroyuki Mori, 2003.Protein translocation across the Escherichia coli plasma membrane is facilitated by concerted actions of the SecYEG integral membrane complex and the SecA ATPase . A secY mutation (secY39) affects Arg357, an evolutionarily conserved and functionally important residue, and impairs the translocation function in vivo and in vitro . In this study, we used the "superactive" mutant forms of SecA, which suppress the SecY39 deficiency, to characterize the mutationally altered SecY39EG translocase . It was found that SecY39-mediated preprotein translocation exhibited absolute dependence on the proton motive force . The proton motive force-dependent step proved to lie before signal peptide cleavage . We suggest that the proton motive force assists in the initiation phase of protein translocation . Biogeochemical Evidence that Thermophilic Archaea Mediate the Anaerobic Oxidation of Methane. Stefan Schouten, 2003.Distributions and isotopic analyses of lipids from sediment cores at a hydrothermally active site in the Guaymas Basin with a steep sedimentary temperature gradient revealed the presence of archaea that oxidize methane anaerobically . The presence of strongly 13C-depleted lipids at greater depths in the sediments suggests that microbes involved in anaerobic oxidation of methane are present and presumably active at environmental temperatures of >30°C, indicating that this process can occur not only at cold seeps but also at hydrothermal sites . The distribution of the membrane tetraether lipids of the methanotrophic archaea shows that these organisms have adapted their membrane composition to these high environmental temperatures .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
