Formation of poliomyelitis subviral particles in the yeast Saccharomyces cerevisiae.

The sequence of the poliovirus genome encoding 3CD (a protease) was transferred to the yeast Saccharomyces cerevisiae on expression vectors with either a constitutive or an inducible promoter. Transformants could only be obtained with vectors carrying the inducible transcription unit. Extracts of induced cells were able to cleave cell-free synthesized P1, the precursor of the poliovirus capsid proteins, into VP0, VP3 and VP1. In yeast cells constitutively expressing P1, induction of 3CD expression resulted in only trace amounts of processed products. Processing could be improved considerably by simultaneous induction of both P1 and 3CD expression. Analysis of extracts of such induced cells revealed the presence of particles that resembled authentic subviral particles.