We demonstrate that the 5' untranslated region (5'UTR) plays an important role in determining translation efficiency in Aspergillus oryzae, using a model beta-glucuronidase (GUS) expression system. Alterations in the 5' UTR resulted in an increase in GUS activity of up to eight-fold, without affecting mRNA levels. Moreover, using the most effective 5'UTR construct, we could achieve remarkable intracellular overproduction of GUS protein; and the GUS level reached more than 50% of the total soluble protein. This is the first experimental evidence indicating the feasibility of improving recombinant protein yield by promoting translation initiation in filamentous fungi.
