Expression of cloned human haptoglobin and alpha 1-antitrypsin complementary DNAs in Saccharomyces cerevisiae
Nucleotide sequences coding either for human preprohaptoglobin or for prohaptoglobin have been placed under the control of yeast ARG3 expression signals. Recombinant plasmids pRIT12598 and pRIT12597 express the prepro- and the pro-form of alpha 2 beta haptoglobin respectively, but at very low levels. Comparison with the expression of human pre- and mature alpha 1-antitrypsin cDNAs, cloned in the same expression vector, reveals large differences in the levels of specific proteins produced in yeast, although specific mRNA levels are similar. It is shown that presence or absence of the signal sequence in the cDNA construction results in a 20- to 30-fold difference in the yields of heterologous products. However, since haptoglobin and alpha 1-antitrypsin behave differently, the difference in expression for prohaptoglobin compared with the expression of mature alpha 1-antitrypsin is about three orders of magnitude. In addition, we provide evidence that glycosylation of both proteins can occur in yeast only when the signal sequence is present in the DNA constructions.