Expression of hepatitis B virus surface antigen in yeast

The structural gene of Hepatitis B virus surface protein (HBsAg) was introduced into a plasmid capable of autonomous replication and selection in both the yeast Saccharomyces cerevisiae and E. coli. In this plasmid transcription of the HBsAg is initiated by the 5′-flanking sequence of the yeast 3-phosphoglycerate kinase (PGK) gene and terminated by the 3′-flanking region of the yeast TRP1 gene. Yeast cells containing this plasmid produce a new major species of mRNA of 1200 nucleotides in length coding for HBsAg. Viral surface antigen is made in nonglycosylated form at a level of about 1–2 percent of total yeast protein. A small fraction of this polypeptide (2-5 percent) is found in aggregated form upon yeast cell disruption by glass beads. This material is similar in size, density, and shape to the 22nm particle, isolated from the plasma of human hepatitis carriers, and induced comparable levels of HBsAg antibodies in mice when compared with the natural particle.