The Cercospora nicotianae CRGI gene is involved in cellular resistance to the perylenequinone toxin, cercosporin, that generates highly toxic singlet oxygen upon exposure to light. The entire open reading frame (ORF) of CRG1 was isolated and sequenced. The gene contains an ORF of 1950bp including a 65-bp intron. The predicted 650 amino acid CRGI protein contains a Cys(6)Zn(2) binuclear cluster DNA-binding motif with homology to various fungal regulatory proteins, indicating that CRGI may act functionally as a transcription activator. Targeted gene disruption of CRGI resulted in mutants that are partially sensitive to cercosporin and reduced in cercosporin production. Genetic complementation revealed that CRGI fully restored cercosporin resistance, but only slightly restored cercosporin production in a UV-derived mutant (CS10) containing a single nucleotide substitution in erg]. Complementation of a crg1-null mutant. however, yielded strains that are similar to the wild-type in both phenotypes. These results indicate that the transcription regulator CRGI is involved in the activation of genes associated with cercosporin resistance and production in the fungus Cercospora nicotianae. (C) 2003 Elsevier Science (USA). All rights reserved.