High level of expression of a protective antigen of schistosomes in Saccharomyces cerevisiae

Abstract
Strains of Saccharomyces cerevisiae expressing P28‐I, an antigen inducing protection against schistosomiasis, have been constructed. Transformants containing a very high copy number of a P28‐I expression vector were selected by genetic complementation involving deficient LEU2 or URA3 alleles carried by plasmids. Using the ura3 fur1 auto‐selection system, constitutive and stable expression of P28‐I could be obtained in cultures grown in rich medium. The accumulation of the foreign protein exceeds 25% of total yeast proteins when estimated by Coomassie Brilliant Blue staining of SDS‐PAGE. Moreover, P28‐I which was located intracellularly was soluble and biologically active.