2 DIVERGENT CATALASE GENES ARE DIFFERENTIALLY REGULATED DURING ASPERGILLUS-NIDULANS DEVELOPMENT AND OXIDATIVE STRESS

Catalases are ubiquitous hydrogen peroxide-detoxifying enzymes that ar e central to the cellular antioxidant response, Of two catalase activi ties detected in the fungus Aspergillus nidulans, the catA gene encode s the spore-specific catalase A (CatA). Here we characterize a second catalase gene, identified after probing a genomic library with catA, a nd demonstrate that it encodes catalase B. This gene, designated catB, predicts a 721-amino-acid polvpeptide (CatB) showing 78% identity to an Aspergillus fumigatus catalase and 61% identity to Aspergillus nige r CatR. Notably, similar levels of identity are found when comparing C atB to Escherichia coli catalase HPII (43%) A. nidulans CatA (40%), an d the predicted peptide of a presumed catA homolog from A. fumigatus ( 43%). In contrast, the last two peptides share a 79% identity. The cat alase B activity was barely detectable in asexual spores (conidia), di sappeared after germination, and started to accumulate 10 h after spor e inoculation, throughout growth and conidiation. The catB mRNA was ab sent from conidia, and its accumulation correlated with catalase activ ity, suggesting that catB expression is regulated at tile transcriptio n level, In contrast, the high CatA activity found in spores was lost gradually during germination and growth. In addition to its developmen tal regulation, CatB was induced by H2O2 heat shock, paraquat, or uric acid catabolism but not by osmotic stress, This pattern of regulation and the protective role against H2O2 offered by CatA and CatB, at dif ferent stages of the A. nidulans life cycle, suggest that catalase gen e redundancy performs the function of satisfying catalase demand at th e two different stages of metabolic and genetic regulation represented by growing hyphae versus spores, Alternative H2O2 detoxification path ways in A. nidulans were indicated by the fact that catA/catB double m utants were able to grow in substrates whose catabolism generates H2O2 .