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CUP2 is a copper-dependent transcriptional activator of the yeast CUP) metallothionein gene. In the presence of Cu+ (and Ag+) ions its DNA-binding domain is thought to fold as a cysteine-coordinated Cu cluster which recognizes the palindromic CUP) that affect amino acids lying between the second pair of cysteines in the first Zn finger of the glucocorticoid and estrogen receptors generate receptors with altered recognition specificity (6,24,40). These residues may therefore participate in contacting the DNA. Although the second finger is essential for DNA binding, its role is unknown (3).A third class of metal-dependent DNA-binding proteins is represented by the CUP2 (also known as ACE1) protein of Saccharomyces cerevisiae (4,11,35

Abstract— Cercosporin, one of a number of 4,9‐dihydroxyperylene‐3,10‐quinones synthesized by plant pathogenic fungi, abundantly produces singlet oxygen when illuminated in solution. Singlet oxygen production is substantially decreased and superoxide production is greatly enhanced in the presence of the reducing agents ergothioneine (2‐thiol‐L‐histidine betaine) or urate. Both ergothioneine and urate enhance superoxide production at a rate approximately 25‐fold that elicited by an equimolar amount of methionine, the agent that is traditionally used in such assays. Such ‘switching’ in production of different active oxygen species under different environmental conditions may be of significance in biological processes, in this case host cell killing by the plant pathogen.

Feline immunodeficiency virus (FIV), like other members of the lentivirus subfamily, such as human immunodeficiency virus type 1 (HIV-1), can infect nondividing and terminally differentiated cells. The transport of the preintegration complex into the nucleus is cell cycle-independent, but the mechanism is not well understood. Integrase is a key component of the complex and has been suggested to play a role in nuclear import during HIV-1 replication. To determine its karyophilic property, FIV integrase fused with glutathione S-transferase and enhanced green fluorescent protein was expressed in various feline and human cells and the subcellular localization was visualized by fluorescence microscopy. Wild-type FIV integrase was karyophilic in all cell lines tested and capable of targeting the fusion protein to the nuclei of transfected cells. Analysis of deletion and point mutation variants of FIV integrase failed to reveal any canonical nuclear localization signal, and the karyophilic determinant was mapped to the highly conserved N-terminal zinc-binding HHCC motif. A region near the C-terminal domain enriched with basic amino acid residues also affected the nuclear import of integrase. However, the role of this region is only modulatory in comparison to that of the zinc-binding domain. The N-terminal zinc-binding domain does not bind DNA and instead is essential in integrase multimerization. We therefore postulate that the karyophilic property of FIV integrase requires subunit multimerization promoted by the HHCC motif. Alternatively, the HHCC motif may directly promote interaction between FIV integrase and cellular proteins involved in nuclear import.

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