Expression of hepatitis B virus core gene products with specific immunoreactivity for e antigen (HBeAg) in Saccharomyces cerevisiae

The e antigen of the hepatitis B virus (HBeAg) was expressed in S. cerevisiae. Yeast-derived HBeAg exhibits high HBe antigenicity while lacking any HBc antigenicity. The production yield of HBeAg expressed in yeast is dependent on the host strains and the nature of the leader sequences used in the plasmid constructions. The recombinant antigen is not secreted into the medium, independent from the leader sequences which are used. A simple extraction procedure was developed, enabling the isolation of HBeAg from the cells without killing them. Recombinant HBeAg derived from yeast can replace plasma-derived antigen in ELISA for determining antibodies to HBeAg.

Expression of the human blood coagulation protein Factor XIIIa in Saccharomyces cerevisiae: dependence of the expression levels from host-vector systems and medium conditions

The human blood coagulation protein Factor XIIIa (FXIIIa) was expressed in Saccharomyces cerevisiae employing Escherichia coli-yeast shuttle vectors based on a 2-mu plasmid. Several factors affecting high production yield of recombinant FXIIIa were analysed. The use of the regulatable GAL-CYC1 hybrid promoter resulted in higher FXIIIa expression when compared with the constitutive ADCI promoter. Screening for suitable yeast strains for expression of FXIIIa under the transcriptional control of the GAL-CYC1 hybrid promoter revealed a broad spectrum of productivity. No obvious correlation between the expression rate and the genetic markers of the strains could be identified. The medium composition markedly influenced the FXIIIa expression rates. The expression of FXIIIa was strictly regulated by the carbon source. Glucose as the only sugar and energy source repressed the synthesis of FXIIIa, whereas addition of galactose induced FXIIIa expression. Special feeding schemes resulted in a productivity of up to 100 mg FXIIIa/l in shake flasks.

New expression vectors for the fission yeast Schizosaccharomyces pombe

A general expression vector (pMB332) for the fission yeast Schizosaccharomyces pombe was constructed. The heterologous gene expression is driven by the S. pombe alcohol dehydrogenase (adh) promoter. Transcription termination signals were isolated from the S. pombe actin gene. The vectors carry the Saccharomyces cerevisiae Ura3 gene, which complements the S. pombe ura4 mutation. The plasmid stability is conferred by the S. pombe ars and stb elements isolated from pFL120 [(1983) Cell 32, 371-377]. An 'ATG' vector (pMB340) was created, which allows the expression of protein fragments fused to a translational start codon downstream of the adh promoter. The function of this vector system is shown by the production of the human blood coagulation protein factor XIIIa.