AN ENDO-1,4-BETA-XYLANASE-ENCODING GENE FROM AGARICUS-BISPORUS IS REGULATED BY COMPOST-SPECIFIC FACTORS

Compost is the preferred substrate for growth of the edible fungus Aga ricus bisporus. Utilization of compost requires the production of enzy mes involved in degradation of lignocellulolytic components. Fur molec ular characterization of these processes we are isolating the encoding genes. By applying heterologous screening techniques,we have cloned s uch a gene, which is specifically induced on compost encoding an endo- 1,4-beta-xylanase (xlnA) belonging to glycosyl hydrolase family 10. Th e gene encodes a pre-protein of 333 amino acid residues with a predict ed molecular mass of 34,946 for the mature protein. The open reading f rame is interrupted by ten introns of which introns 5 and 6 are separa ted by an exon of only two base-pairs, High expression of the xlnA gen e was observed in vegetative mycelium grown on sterilized compost whil e xlnA messengers were not detected in fruit bodies. Addition of gluco se or xylose to compost repressed xlnA expression. When glucose-grown colonies were transferred to a medium containing cellulose, xylan or x ylose as sole carbon source, the organism responded by expressing xlnA at a high level for a short period. Transfer from glucose to compost yielded a much stronger and constant xlnA induction. A similar pattern of expression was found for the cel3 gene encoding a cellulase, sugge sting that these genes are induced by compost-specific factors rather than by the substrates they act upon. Antiserum raised against XLNA pr otein, which was heterologously expressed in Escherichia coli, detecte d, when the fungus was grown on compost, an extracellular protein of 3 3 kDa with endo-xylanase activity. (C) 1998 Academic Press Limited.