Assembly of hepatitis delta virus-like empty particles in yeast

Large delta antigen (L-HDAS) of hepatitis delta virus (HDV DV) and small-form hepatitis B surface antigen (HBsAS) of helper hepatitis 3 virus have previously been shown to be the minimum components for the assembly of HDV-like particles in mammalian cells. Extending from this finding, we coexpressed L-HDAS and small HBsAg in Saccharomyces cerevisiae to study their assembly in yeast cells. The assembly of virus particles from L-HDAg and HBsAS in yeast was demonstrated by their coexistence in the same isopycnic fractions and by the coimmunoprecipitation of L-HDAS with HBsAS using an antibody against HBsAS (anti-HBs). Furthermore, after purification by affinity chromatography with anti-HBs, HDV-like particles with size and morphology similar to those derived from mammalian cells could be visualized by electron microscopy. Mice immunized with yeast-derived HDV-like particles simultaneously acquired antibodies against HBsAg and HDAg, indicating that both viral proteins are antigenic. The results indicated that S. cerevisiae could serve as a host for the assembly of HDV-like empty particles. This system may be useful in investigating cellular processes involved in HDV assembly and in producing ample amount of HDV-like particles for structural and immunological studies.