High yield synthesis of the bovine leukemia virus (BLV) p24 major internal protein in Saccharomyces cerevisiae.

Bovine leukemia virus (BLV) p24 gene was expressed in Saccharomyces cerevisiae under the control of the PHO5 (encoding repressible acid phosphatase, rAPase) promoter. Yeast cells were transformed by a yeast-E. coli shuttle vector carrying the PHO5 promoter, the p24 gene and the CYC1 transcription terminator. After low inorganic phosphate (Pi) induction of the PHO5 promoter, p24 accumulated in the producing cells up to a concentration representing 10% of total soluble proteins. The expression level of p24 gene was not increased by insertion of the positive regulatory gene PHO4 on the p24 expression vector. The p24 produced in this system and incubated in crude yeast extract showed a remarkably high resistance to proteolytic degradation, a feature that presumably correlates with the compact globular conformation of the protein combined to the stabilizing effect of the N-terminal residue.