The cel4 gene of Agaricus bisporus encodes a beta-mannanase

Mannases have industrial uses in food and pulp industries, and their regula tion may influence development of the mushrooms of commercially important b asidiomycetes. We expressed an Agaricus bisporus cell cDNA, which encodes a mannanase, in Saccharomyces cerevisiae and Pichia pastoris, CEL4 had no de tectable activity on cellulose or xylan. This gene is the first isolated fr om this economically important fungus to encode a mannanase, P. pastoris se creted about three times more CEL4 than S. cerevisiae. The removal of the c ellulose-binding domain of CEL4 lowered the secreted specific activity by P , pastoris by approximately 97%. The genomic sequence of cell was isolated by screening a cosmid library of A. bisporus C54-carb8. The open reading fr ame was interrupted by 12 introns. The level of extracellular CEL4 increase s dramatically at the postharvest stage in compost extracts of A. bisporus fruiting cultures. In laboratory liquid cultures of A. bisporus, the activi ty of CEL4 detected in the culture filtrate reached a maximum after 21 days , The levels of CEL4 broadly mirrored the levels of enzyme activity. In the Solka hoc-bound mycelium, CEL4 protein showed a maximum after 2 to 3 weeks of culture and then declined. Changes in CEL4 activity during fruiting-bod y development suggest that hemicellulose utilization plays an important rol e in sporophore formation. The availability of the cloned gene will further studies of compost decomposition and the extracellular enzymes that fungi deploy in this process.