A method for producing a transgenic cell product comprising: (a) providing an expression system comprising: a methylotrophic yeast cell comprising an expression vector, said expression vector comprising an inducible MUT (Methanol Utilization) pathway promoter operably linked to a nucleic acid molecule encoding a recombinant protein of interest for producing a transgenic cell product of interest, wherein the inducible MUT promoter is selected from the group consisting of: NAD+-dependent formate dehydrogenase promoter; alcohol oxidase 2 promoter; dihydroxyacetone kinase promoter; dihydroxyacetone synthase 1,2 (DAS1,2) promoter; formaldehyde dehydrogenase 1 promoter; Fructose 1,6-bisphosphate aldolase promoter; Peroxisomal membrane signal receptor PTS1 promoter; and catalase promoter; (b) growing the methylotrophic yeast cell on a suitable carbon source for supporting active growth of the methylotrophic yeast cell and for repressing the inducible MUT pathway promoter, thereby providing a methylotrophic yeast cell culture; (c) after the methylotrophic yeast cell culture has attained a suitable methylotrophic yeast cell culture density, growing the methylotrophic yeast cell culture on a non-repressing carbon source selected from the group consisting of: sorbitol, mannitol, trehalose and alanine, thereby de-repressing the inducible MUT pathway promoter; (d) adding an amount of an inducer compound selected from the group consisting of: S-formylglutathione; S-hydroxymethyl glutathione; formic acid; an alkali metal salt of formic acid; and an alkaline earth metal salt of formic acid; sufficient to induce the inducible MUT pathway promoter to the methylotrophic yeast cell culture such that the inducible MUT pathway promoter expresses the nucleic acid molecule encoding the recombinant protein of interest, thereby producing the transgenic cell product of interest; and (e) recovering the transgenic cell product of interest from the methylotrophic yeast cell culture. (a) providing an expression system comprising: a methylotrophic yeast cell comprising an expression vector, said expression vector comprising an inducible MUT (Methanol Utilization) pathway promoter operably linked to a nucleic acid molecule encoding a recombinant protein of interest for producing a transgenic cell product of interest, wherein the inducible MUT promoter is selected from the group consisting of: NAD+-dependent formate dehydrogenase promoter; alcohol oxidase 2 promoter; dihydroxyacetone kinase promoter; dihydroxyacetone synthase 1,2 (DAS1,2) promoter; formaldehyde dehydrogenase 1 promoter; Fructose 1,6-bisphosphate aldolase promoter; Peroxisomal membrane signal receptor PTS1 promoter; and catalase promoter; (b) growing the methylotrophic yeast cell on a suitable carbon source for supporting active growth of the methylotrophic yeast cell and for repressing the inducible MUT pathway promoter, thereby providing a methylotrophic yeast cell culture; (c) after the methylotrophic yeast cell culture has attained a suitable methylotrophic yeast cell culture density, growing the methylotrophic yeast cell culture on a non-repressing carbon source selected from the group consisting of: sorbitol, mannitol, trehalose and alanine, thereby de-repressing the inducible MUT pathway promoter; (d) adding an amount of an inducer compound selected from the group consisting of: S-formylglutathione; S-hydroxymethyl glutathione; formic acid; an alkali metal salt of formic acid; and an alkaline earth metal salt of formic acid; sufficient to induce the inducible MUT pathway promoter to the methylotrophic yeast cell culture such that the inducible MUT pathway promoter expresses the nucleic acid molecule encoding the recombinant protein of interest, thereby producing the transgenic cell product of interest; and (e) recovering the transgenic cell product of interest from the methylotrophic yeast cell culture.