Summary: Among secreted proteins of 168 four polypeptides, separated by electrophoresis in polyacrylamide gradient gels under denaturing conditions, were shown to have lichenanhydrolysing enzyme activity; one of them, a 22 kDa protein, represents the main β-glucanase activity. A number of -methyl--nitro--nitrosoguanidine-induced mutants defective in β-glucanase activity at an elevated temperature (44°C) were isolated and characterized. All mutants analysed by PAGE had no active 22 kDa β-glucanase in their supernatants and showed no cross-reactivity with antibodies raised against purified 22 kDa β-glucanase. However, formation of other exoenzymes, including the other minor β-glucanases, was not affected in these mutant strains. The mutations () were mapped by phage PBS1-mediated transduction and found to be located between and , close to the marker of the chromosome. A 3.8 kb RI fragment of the chromosome which directs β-glucanase synthesis in as well as complementing a β-glucanase deficient mutant, , of to synthesize active 22 kDa β-glucanase was mapped after homologous recombination by means of an integratable plasmid. The cointegrated chloramphenicol-resistance marker of the plasmid was found at the same map position as the mutations and , suggesting that the gene affected encodes for the 22 kDa β-glucanase and lies within the order


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