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Analysis of binding sites for the nitrogen-control transcription factor NtcA in the promoters of Synechococcus nitrogen-regulated genes.

Dissociation constant (K(d)) was determined for the binding of the transcriptional regulator NtcA to a number of NtcA-activated promoters of the cyanobacterium Synechococcus sp. PCC 7942, as well as to mutant versions of those promoters altered in their NtcA-binding sites. K(d) values obtained ranged from 27 nM for the NtcA-binding site in the glnA promoter to ca. 1.4 microM for the site in the glnB promoter. Changes in the sequence signature of NtcA-binding sites (i.e. GTAN(8)TAC) either completely prevented binding of NtcA or drastically decreased its affinity for the promoter revealing that the GTN(10)AC subset is essential for binding. The importance of the flanking A/T-rich sequences and of a conserved CA dimer found in between the GTA/TAC triplets was also stressed. Thus, this structure seems to be optimal for the binding of NtcA. Comparison of K(d) values for NtcA binding to native promoters showed that differences in the sequence of their NtcA binding sites determine extensive differences in the affinity of the regulator for those sites.

Amino Acid Sequence↗

Phosphorus-nitrogen-phosphorus ligands: cooperative effects between nitrogen and phosphorus substituents on catalytic activity.

A new generation of PNP compounds bearing different diarylphosphine groups were prepared and used as ligands in palladium-catalysed Suzuki cross-coupling reactions. Rates of oxidative addition of iodobenzene to (PNP)Pd[0] complexes were measured using UV spectroscopy. Synergistic effects between the N- and P- substituents were identified and correlated in redox and catalytic chemistry.

Journal Article↗

Lithium-nitrogen and lithium-boron-nitrogen cage compounds formed using the phenylhydrazido backbone.

Two rare examples of the crystal structures of large molecular clusters formed from the lithium salts of multianions are reported; the first is the dilithium salt of phenylhydrazine, which forms a tetrameric cage with a core of eight Li and eight N centres; the second is a 32-membered cage which forms from the aggregation of two [B(NNPh)3]6- hexaanions, two [NH-NPh]2- dianions and 16 Li+ cations.

Journal Article↗