Cloning of an acidic laccase gene (clac2) from Coprinus congregatus and its expression by external pH

Coprinus congregatus synthesized and secreted high amounts of laccase under acidic culture condition (pH 4.1) transiently. We have cloned a genomic DNA fragment between the copper binding regions I and II of a laccase by PCR from C. congregatus. This fragment was used as a probe to clone a laccase cDNA from the acidic culture. The cDNA (clac2) consisted of 1817 bp which contains 1086 bp encoding 362 amino acids. The N-terminal sequence of the purified CLAC2 revealed that the first 16 amino acids were removed by the modification. The purified protein had two copper binding regions, although other fungal laccases had four. According to a Northern blotting analysis the clac2 was expressed not in neutral culture but in acidic culture only. The transcription of the clac2 as well as the laccase activity reached a maximum after 24 h upon transferring to an acidic culture, and then decreased very rapidly.