Paul Sabatier University

About: Paul Sabatier University is a education organization based out in Toulouse, France. It is known for research contribution in the topics: Population & Catalysis. The organization has 15431 authors who have published 23386 publications receiving 858364 citations.

An rpsL Cassette, Janus, for Gene Replacement through Negative Selection in Streptococcus pneumoniae

Abstract: Natural genetic transformation offers a direct route by which synthetic gene constructs can be placed into the single circular chromosome of Streptococcus pneumoniae. However, the lack of a general negative-selection marker has hampered the introduction of constructs that do not confer a selectable phenotype. A 1.3-kb cassette was constructed comprising a kanamycin (Kn) resistance marker (kan) and a counterselectable rpsL(+) marker. The cassette conferred dominant streptomycin (Sm) sensitivity in an Sm-resistant background in S. pneumoniae. It was demonstrated that it could be used in a two-step transformation procedure to place DNA of arbitrary sequence at a chosen target site. The first transformation into an Sm-resistant strain used the cassette to tag a target gene on the chromosome by homologous recombination while conferring Kn resistance but Sm sensitivity on the recombinant. Replacement of the cassette by an arbitrary segment of DNA during a second transformation restored Sm resistance (and Kn sensitivity), allowing construction of silent mutations and deletions or other gene replacements which lack a selectable phenotype. It was also shown that gene conversion occurred between the two rpsL alleles in a process that depended on recA and that was susceptible to correction by mismatch repair.

Remarks on the Proper Use of the Broken Symmetry Approach to Magnetic Coupling

Abstract: The effect of nonorthogonality in the broken symmetry approach to magnetic coupling has been explicitly considered for the first time in Hartree−Fock and a variety of DFT methods. On the basis of the results for three different systems, representative of a variety of physical situations it is shown that the most often quoted trend concerning the much larger degree of delocalization of magnetic orbitals obtained from DFT, as opposed to Hartree−Fock, is not fully justified. A new and simple way to relate the overlap integral entering into the calculation and the spin density is proposed and tested in a variety of model systems.