ABSTRACT
Heterologous protein expression was the impetus for the development of recombinant DNA technologies in the late 1970s. In the early 1980s, Escherichia coli and Saccharomyces cerevisiae expression systems were developed and used for foreign protein expression [1]. Several comprehensive reviews of these two expression systems are available [2-7]. Development of other expression systems, such as heterologous protein expression in methylotrophic yeasts [8,9] and filamentous fungi [10], followed quickly, and the broad utility of these systems is becoming increasingly apparent.
