Introns are necessary for mRNA accumulation in Schizophyllum commune

The cDNA coding sequence of the Agaricus bisporus hydrophobin gene ABH1 und er the regulation sequences of the Schizophyllum commune SC3 hydrophobin ge ne gave no expression in S. commune. In contrast, the genomic coding sequen ce (containing three introns) produced high levels of ABH1 mRNA when transf ormed to S. commune in the same configuration, Apparently, introns were nee ded for the accumulation of mRNAs from the ABH1 gene, When the effect of in tron deletion on expression of the homologous genes SC3 and SC6 was examine d, it was observed that only the genomic coding sequences were expressed in S. commune, Run-on analysis with nuclei harbouring intron-containing and i ntronless SC6 showed that this effect did not occur at the level of transcr iption initiation: genomic and cDNA sequences were equally active in this r espect. When a 50 bp artificial intron containing the consensus splice and branch sites of S, commune introns, in addition to random-generated sequenc es, was introduced in the right orientation into the intronless SC3 transcr iptional unit, accumulation of SC3 mRNA was restored. By polymerase chain r eaction amplification, no unspliced SC3 mRNA species could be detected, Fur thermore, the addition of an intron into the transcriptional unit of the ge ne for green fluorescent protein (GFP) effected clear fluorescence of the t ransgenic hyphae. Apparently, splicing is required for the normal processin g of primary transcripts in S. commune.