Molecular cloning of a gene abundantly expressed during fruiting body initiation in Schizophyllum commune

Complementary DNA was synthesized on polyadenylated RNA from a dikaryotic mycelium of the basidiomycete Schizophyllum commune bearing fruiting body initials. The complementary DNA was cloned into the PstI site of pBR327 by the deoxyguanidylate-deoxycytidylate tailing approach. After transformation into Escherichia coli cells, a differential screening was performed by colony hybridization with complementary [32P]DNA made on the RNAs of the monokaryon and dikaryon strains. Two clones were selected for further analysis by Northern blotting and hybrid release translation. Clone 1D10 hybridized with an mRNA of 775 nucleotides, coding for a polypeptide with an Mr of 15,000. Although this RNA was present in both monokaryotic and dikaryotic mycelia, its concentration appeared to change considerably over time and with different cultivation conditions. This mRNA is probably the most abundantly expressed sequence in S. commune. Clone 1G2 and its homologs hybridized with an mRNA of 650 nucleotides, coding for a polypeptide with an Mr of 13,000. This gene was exclusively expressed in the dikaryon strain. In liquid-grown cultures, the concentration of this mRNA was low but increased ca. 20-fold during the establishment of fruiting body primordia. A chromosomal fragment of 9 kilobase pairs which contained the 1G2 gene was cloned into pBR327 and used as a probe in Northern blot hybridization. It was found that surrounding sequences were not expressed at the same time or to the same extent as the 1G2 gene.