Transcriptional and post-transcriptional events affect the production of secreted hen egg white lysozyme by Aspergillus niger.

The relationship between heterologous gene copy number, mRNA and secreted protein yields has been studied in Aspergillus niger transformants containing either the hen egg-white lysozyme (HEWL) cDNA gene or a glucoamylase-HEWL gene fusion (incorporating the A. niger glaA gene). The results support a direct relationship between HEWL gene copy number, mRNA and secreted HEWL protein levels at low (< 25) copy numbers. High protein yields are associated with multiple copies of the recombinant gene at a single site. Fusion of the HEWL gene to the glucoamylase gene resulted in higher steady-state levels of heterologous mRNA. Transformants with the HEWL cDNA alone exhibited a ten-fold higher mRNA:protein ratio than transformants with the gene fusion indicating that post-transcriptional events significantly affect final secreted protein yields.