Production of hepatitis B virion-like particles in yeast

We constructed a yeast strain that simultaneously expresses four genes encoding the major S, middle S, large S hepatitis B viral envelope proteins and the core protein under the control of the yeast glyceraldehyde-3-phosphate dehydrogenase promoter and terminator. The lysate from this cell line, examined by immunological, physicochemical methods and electron microscopy, was found to contain spherical particles with a diameter of about 40 nm and a density of 1.25 g/ml. These particles reacted with anti-envelope antibodies, but not with anti-core antibodies. However, core antigenicity appeared upon treatment with 3% Nonidet P-40 that eliminates an outer envelope. These observations suggest production of a virion-like complex structure, or at least its DNA-less analog, consisting of core particle enveloped by antibody-reactive envelope. Such a structure was made only when all the four gene products were synthesized in a yeast cell. This system may be useful for the study of virus structure and assembly, and for improved vaccine development.