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The efficiencies of incision catalyzed by the UvrABC system of two DNA duplexes containing identical (+)-trans-B[a]P-[N.sup.2]-dG adducts embedded in two different sequence contexts are investigated. This study helps in gaining better understanding of the fundamental principles underlying base sequence effects on nucleotide excision repair.

A potential novel function of xeroderma pigmentosum group( XPA) in nucleotide excision repair (NER) to stabilize the unwound DNA intermediate surrounding the lesion using a homogeneous form of XPA purified from baculovirus-infected calls is studied. It is proposed that XPA plays a significant role in stabilizing, via its high affinity to ds-ssDNA junctions, the DNA strand opening surrounding the lesion for stable formation of preincision NER intermediates.

The spectroscopic and computational studies about the effect of the base sequences on stacked (S) versus B-type (B) conformational heterogeneity caused by the major dG adduct derived from the model carcinogen 7-fluoro-2-aminofluorene (FAF) is reported. The findings show that FAF-modified DNA duplexes balanced between S and B conformations and interconverted slowly at room temperature.

The structural features of human replication protein A (RPA) interaction with single-stranded (ssDNA) are examined by using fluorescence spectroscopy. A global structure model is proposed for binding of the major RPA DNA binding domains (DBDs) to ssDNA.

Escherichia coli nucleotide excision repair (NER) enzymes UvrA, UvrB and UvrC were employed to examine the incision efficiency of duplex DNA carrying three different oxidative intrastrand cross-link lesions and tow dithymine photoproducts. The results showed that T[6-4]T was the best substrate for UvrA binding, followed by G[8-5]C, G[8-5m]mC and G[8-5m]T and then T[c,s]T and this suggests that oxidative intrastrand lesions might be substrates fro NER enzymes in vivo.

The oligomeric interactions of homogenous human xeroderma pigmentosum group A (XPA) protein with the 50-bp DNA substrate containing a single acetyl-2-aminofluorene (AAF)-DNA are characterized. The results suggest that the XPA dimer is probably the major form of the protein involved in the DNA damage recognition.

A single mutation of Y95W that enhances the binding of UvrB to structure-specific DNA adducts without the participation of UvrA, while mutations at other nearby aromatic and hydrophobic sites in the beta-hairpin did not exhibit any enhancement in binding are demonstrated. According to the results, the Y95 residue plays a unique role in stabilizing the interaction of UvrB with DNA damage by hydrophobic stacking.

The fluorescence spectroscopy is adopted to investigate the biochemical properties and thermodynamics of DNA damage recognition by the mutant protein. The binding of the UrvB (Y95W) mutant protein to a structure-specific 30 bp DNA substrate containing a single flurescein, which acts as both an adduct and a fluorophore, is examined.

A sequential Diels-Alder reaction/rearrangement sequence was developed for the synthesis of diverse functionalized bicyclo[2.2.1]heptanes as novel floral and woody odorants. The outcome of the rearrangement depended on the substitution pattern of the dienes. 2D NMR analysis has established the correct relative configuration of the bicyclo[2.2.1]heptanone, which was originally misassigned. Furthermore, when the initiating DA reaction was catalyzed by a chiral Lewis acid, the bicyclo[2.2.1]heptane derivatives including (+)-herbanone can be obtained in an enantiomeric ratio (er) up to 96.5:3.5. [ABSTRACT FROM AUTHOR]

An unexpected gold(l)-catalyzed homo-Rautenstrauch rearrangement of 1-cyclopropyl propargylic esters to cydohexenones is disclosed. This rearrangement represents new evidence for the recently discussed gold-stabilized non-classical carbocation character of intermediates in gold catalysis. A mechanistic study proved partial chirality transfer from optically active propargyl acetates. [ABSTRACT FROM AUTHOR]

Examines the hierarchy of DNA damage recognition in nucleotide excision repair in Escherichia coli. Differentiation between initial and second recognition; Role of adenosine triphosphate in DNA damage recognition; Factors influencing the incision efficiency of UvrABC.

Examines the differential incision of bulky carcinogen-DNA adducts by the UvrABC nuclease. Importance of Escherichia coli UvrABC nuclease system in the removal of DNA damages; Account on UvrABC proteins interaction in DNA lesion sites; Influence of different adducts on UvrA binding affinities; Extent of UvrB-DNA complex formation.