EXPRESSION OF ESCHERICHIA-COLI FOLYLPOLYGLUTAMATE SYNTHETASE IN THE CHINESE-HAMSTER OVARY CELL MITOCHONDRION

Chinese hamster ovary (CHO) cell transfectants expressing Escherichia coli folylpoly-gamma-glutamate synthetase (FPGS) activity solely in th eir cytosol lack mitochondrial folylpolyglutamates and are auxotrophic for glycine. Addition of a mammalian mitochondrial leader sequence ta rgeted E. coli FPGS to the mitochondria of these cells. Mitochondrial expression of FPGS restored mitochondrial folylpolyglutamate pools and overcame the glycine requirement. Pteroyltriglutamates functioned as effectively as the longer glutamate chain length folates found in wild type CHO cells in the metabolic cycle of glycine synthesis provided t hey were located in the mitochondria. Although folylpolyglutamates can not enter the mitochondria, mitochondrial folylpolyglutamates can be r eleased without prior hydrolysis and CHO transfectants expressing E. c oli FPGS activity solely in the mitochondria possessed normal cytosoli c folylpolyglutamate pools. The proportion of cellular folate in the m itochondrion is governed by competition between mitochondrial and cyto solic FPGS activities.