RESUMO
A gene-fusion expression strategy was applied for heterologous expression of human lymphotoxin alpha (LTalpha) in the Aspergillus niger AB1.13 protease-deficient strain. The LTalpha gene was fused with the A. niger glucoamylase GII-form as a carrier-gene, behind its transcription control and secretion signals. Special attention was paid to the influence of different codon usage on secretion of protein. In the case of human tumor necrosis factor alpha (TNFalpha) a dramatic change of secretion has been observed when human cDNA sequence was used instead of synthetic E. coli biased codons. In the case of LTalpha such a change of codon usage brought improvement at the RNA level, however, no increase in the quantity of secreted protein was observed, due to the proteolitic activity of the host organism. The estimated yield of secretion of LTalpha from A. niger into the soya medium was 50 pg l(-1) of culture.