SummarycitS and citT genes encoding a new two-component system were identified in the 718 region between the pel and citM loci on the Bacillus subtilis chromosome. citS-and citT-deficient strains were unable to grow on minimal plates including citrate as a sole carbon source. In addition, a strain deficient in citM, which encodes the secondary transporter of the Mgcitrate complex, exhibited the same phenotype on this medium. Northern blot analysis revealed that citM was polycistronically transcribed with the downstream yflN gene, and that CitS and CitT were necessary for transcription of the citM±yflN operon. Upon addition of 2 mM citrate to DSM, this operon was strongly induced after the middle of the exponential growth phase in the wild type, but not in the citST double null mutant. Moreover, the transcription of this operon was completely repressed in the presence of 1% glucose. We found a sequence exhibiting homology to a catabolite-responsive element (cre) in the citM promoter region. Glucose repression was lost in ccpA and citM±cre mutants. From the result of a citM±promoter deletion experiment, putative CitT target sequences were found to be located around two regions, from 262 to 274 and from 2149 to 2189, relative to the citM start point. Furthermore, DNase I footprinting assays revealed that these two CitT target regions extended maximally from 236 to 284 and from 2168 to 2194. From these findings, we concluded that the expression of citM is positively regulated by the CitST system and negatively regulated by CcpA.

We have performed molecular-dynamics simulations using realistic many-body semiclassical potentials for hydrosilicon interactions to investigate the deposition and diffusion dynamics of thermal to hyperthermal SiH3 radicals on hydrogen-terminated silicon (100) surfaces. We have studied the radical diffusion length as a function of difFerent incident radical energies to know the efFect of the radical energization on the radical diffusion upon a substrate. As a result of the deposition and diffusion dynamics simulation using 100 radicals, it was observed that when radicals having an incident kinetic energy of about 700 K adsorb vertically on a substrate with high hydrogen coverage, the average diffusion length is 0 the largest and the value is about 32 A. It was found that the incident energized radical has an optimum energy to maximize the radical diffusion length on a substrate under some conditions.

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The tetrazolo-azido transformation for eight model compounds (3, 4a-c, 5-8) are discussed. The tetrazoloazido equilibrium in 3a,b is much influenced by the solvent, but the pyridazine derivatives (4a-c) exist entirely as the tetrazoles in various solvents. Compounds 5 and 6 are demonstrated to exist exclusively as the azido form in the solid state because of the destabilization of the fused rings by electron-attracting tetrazolo and triazolo moieties. The tetrazolo-azido equilibrium in as-triazine derivatives 7 and 8 is observed in chloroform, but the tetrazolo form is predominant. Photochemical and thermal reactions of 3 give the imidazoles.

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