New method for the selection of multicopy transformants of Pichia pastoris, using 3-amino-1,2,4 triazol

The methylotrophic yeast Pichia pastoris has been successfully used for the expression of many heterologous proteins. The level of expression of some of these proteins depends on the copy number of the gene inserted into the yeast genome. Several methods have been reported in the past few years for the isolation of multicopy transformants. One of these methods used an expression vector that contains the bacterial kanamycin-resistance gene Tn903kanr, which confers resistance to G418. Here, we report a different selection method in a mutant strain of P. pastoris (his3-) based on the resistance to 3-amino-1,2,4 triazol, with a vector containing the HIS3 gene from Saccharomyces cerevisiae. Using this selection method, we isolated here P. pastoris transformants containing several copies of the dextranase gene (dex) from Penicillium minioluteum.