|
|
|
|
|
|
Emergence in Italy of a Neisseria meningitidis Clone with Decreased Susceptibility to Penicillin. Paola Stefanelli, 2004.A rise in invasive diseases due to Neisseria meningitidis C:2b:P1.5 with decreased penicillin susceptibility occurred in Italy during the last 2 years . Real-time PCR identified the Peni phenotype, and the penA sequence revealed the mosaicism of the gene . Molecular analyses assigned the isolates to a single emergent clone of the hypervirulent A4 cluster . Natural Transformation and DNA Uptake Signal Sequences in Actinobacillus actinomycetemcomitans. Ying Wang, 2002.Actinobacillus actinomycetemcomitans is a member of the family Pasteurellaceae and a major causative agent of periodontitis . While several genera from this family are known to be competent for transformation, A . actinomycetemcomitans has yet to be fully characterized . Here we show that the competence of A . actinomycetemcomitans is remarkably similar to that of Haemophilus influenzae . In addition to having a similar frequency of transformation as H . influenzae, A . actinomycetemcomitans competence could also be induced at least 100-fold by cyclic AMP, suggesting that, as in H . influenzae, at least some competence genes are regulated by catabolite repression . Even more intriguing was the discovery of a putative A . actinomycetemcomitans DNA uptake signal sequence (USS) virtually identical to the USS of H . influenzae . Moreover, we provide evidence that this sequence functions in the same capacity as that from H . influenzae; the sequence appears to be required and sufficient for DNA uptake in a variety of assays . Finally, we have taken advantage of this system to develop a simple, highly efficient competence-based method for generating site-directed mutations in the wild-type fimbriated A . actinomycetemcomitans . Mutational Analysis of a Conserved Signal-Transducing Element: the HAMP Linker of the Escherichia coli Nitrate Sensor NarX. J. Alex Appleman, 2003.The HAMP linker, a predicted structural element observed in sensor proteins from all domains of life, is proposed to transmit signals between extracellular sensory input domains and cytoplasmic output domains . HAMP (histidine kinase, adenylyl cyclase, methyl-accepting chemotaxis protein, and phosphatase) linkers are located just inside the cytoplasmic membrane and are projected to form two short amphipathic  -helices (AS-1 and AS-2) joined by an unstructured connector . The presumed helices are comprised of hydrophobic residues in heptad repeats, with only three positions exhibiting strong conservation . We generated missense mutations at these three positions and throughout the HAMP linker in the Escherichia coli nitrate sensor kinase NarX and screened the resulting mutants for defective responses to nitrate . Most missense mutations in this region resulted in a constitutive phenotype mimicking the ligand-bound state, and only one residue (a conserved Glu before AS-2) was essential for HAMP linker function . We also scanned the narX HAMP linker with an overlapping set of seven-residue deletions . Deletions in AS-1 and the connector resulted in constitutive phenotypes . Two deletions in AS-2 resulted in a novel reversed response phenotype in which the response to ligand was the opposite of that seen for the narX+ strain . These observations are consistent with the proposed HAMP linker structure, show that the HAMP linker plays an active role in transmembrane signal transduction, and indicate that the two amphipathic
-helices have different roles in signal transduction .
History of the ADP/ATP-Translocase-Encoding Gene, a Parasitism Gene Transferred from a Chlamydiales Ancestor to Plants 1 Billion Years Ago. Gilbert Greub, 2003.Nonmitochondrial ADP/ATP translocase is an energy parasite enzyme . Its encoding gene, tlc, is found only in Rickettsiales, Chlamydiales, and plant and alga plastids . We demonstrate the presence of tlc in Parachlamydia acanthamoebae. This gene shares more similarity with the tlc1 gene of Chlamydiaceae and the tlc of plant and alga plastids than with the tlc2 gene of Chlamydiaceae . Phylogenetic analysis, including all other tlc homologs found in GenBank, showed that tlc was duplicated in a Chlamydiales ancestor before the appearance of multicellular eukaryotes . A time scale, calibrated with seven independent time points obtained from fossil estimates and from the 16S rRNA molecular clock, was congruent with the molecular clock provided by tlc . Plant and alga plastids acquired tlc approximately when Parachlamydiaceae and Chlamydiaceae diverged, at the eucaryotic radiation time, ca . 1 billion years ago .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
