Recombinant hepatitis B virus surface antigen P31 accumulates as particles in Saccharomyces cerevisiae

Saccharomyces cerevisiae harboring expression plasmids for hepatitis B virus surface antigen (HBsAg) P31 and two of its muteins were cultivated in a chemically defined medium. The production of one of the muteins (M–P31d) was more than three times higher than that of the wild–type protein, though the construction of the expression plasmids was the same. Electron microscopic observations provide evidence that HBsAg M–P31d accumulated as particles of 20–30 nm and formed inclusion bodies in the S. cerevisiae cells.