The present invention intends to find out a gene participating in addition of mannose phosphate to a sugar chain of a glycoprotein originating in a yeast belonging to the genus Pichia and provide a means of controlling the same. The present invention also intends to provide a process for producing a protein with reduction of an acidic sugar chain by using the thus controlled yeast strain belonging to the genus Pichia. Namely, the present invention includes a protein participating in the addition of mannose phosphate to a sugar chain of a glycoprotein; a gene encoding this protein; a mutant of this gene; a vector carrying the mutant gene; a yeast strain belonging to the genus Pichia having been transformed by this vector; a process for producing a protein with reduction of an acidic sugar chain by using the transformed yeast strain; and a glycoprotein thus produced.