The DNA sequence located between mecA, the gene that codes for penicillin-binding protein PBP2', and insertion sequence-like element IS431mec has been termed hypervariable because of its length polymorphism among different staphylococcal isolates. We sequenced and characterized the hypervariable region of the methicillin resistance determinant (mec) isolated from Staphylococcus aureus BB270. Within the 2,040-bp hypervariable region, we identified an unusual accumulation of long direct repeats. Analysis of the DNA sequence revealed a minimal direct repeat unit (dru) of 40 bp which was repeated 10 times within 500 bp. The dru sequences are responsible for the length polymorphism of mec. Moreover, we identified an open reading frame that codes for 145 amino acids (0RF145), whose deduced amino acid sequence showed 57% amino acid sequence similarity to the N terminus of the glycerophosphoryl diester phosphodiesterase (UgpQ) of Escherichia coli.

SummaryTransition metal complexes often have low-lying excited electronic states and, as a consequence, tend to be electronically labile, i.e., their electronic properties exhibit pronounced sensitivity to external perturbations. Often drastic changes in various spectroscopic properties indicating substantial electronic rearrangements can be induced by relatively weak intermolecular forces as provided by nonpolar solvents or solid molecular host lattices. This behaviour can be explained by crossing of potential surfaces in the vicinity of the absolute minimum. Many physical properties of a given orbitally (near-) degenerate system depend strongly on the relative magnitude of some characteristic parameters determining the shape of the ground Born-Oppenheimer potential surface(s), e.g. barrier height versus zero-point energy, distance between minima versus zero-point amplitude, energy difference between minima, etc. Typical examples are systems exhibiting JahnTeller activity, spin-crossover, mixed valence, exchange coupling and other types of electronic near-degeneracies. In paramagnetic systems changes in the electronic wavefunction can be most conveniently detected and analyzed by using EPR. spectroscopy.In paramagnetic sandwich complexes we studied two types of orbital degeneracies: Jahn-Teller degeneracies (d7-systems such as Co (CP)~, Ni (cp)? and Fe (cp) (bz), low-spin d5-systems such as Mn (CP)~) and low-spin/high-spin equilibria (d5-systems such as Mn (cp)Z). By diluting these complexes and ring-substituted derivatives in a large variety of diamagnetic host systems we have been able to control the 6A/2E equilibrium of Mn ( C P )~ by influencing the metal-to-ring distance and by changing the degree of ring alkylation; similarly we have been able to vary the relative weights of the two electronic states contributing to the two-fold degenerate electronic ground state of d5-and d7-systems to a large degree by variation of the local asymmetric fields offered by the lattice sites of the host systems.For comparison the electronic ground state properties of octahedral Cu (11) also studied by EPR. between 4K and room temperature in several host systems. Characteristic differences in the details of the temperature and host dependence of the EPR. spectra in all these electronically labile systems can be explained in terms of differences in the vibronic coupling type ( E 0 e vs. T 6) e, t), the strength of linear and/or quadratic JT-coupling and the effects produced by spin-orbit coupling.

This pair can either collapse to the regular adduct6 or diffusively separate to form Pt'-X and R•. Depending on the reactivity of the reactant alkyl halide, two pathways may then develop. For very reactivé halides (as are described in this communication), Pt'-X can rapidly abstract further halide to yield dihalide and organic radical. CIDNP effects result from the diffusive encounter of these product radicals. Alternatively, for less reactive halides, the organic radical will initiate a chain process to produce regular adduct (and/or hydrido complex).

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