A MUTATION IN GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE ALTERS ENDOCYTOSIS IN CHO CELLS

The CHO cell mutant FD1,3.25 exhibits both increased accumulation and altered distribution of endocytosed fluid phase tracers. Neither the r ate of tracer internalization nor the kinetics of recycling from early endosomes was affected, but exocytosis from late endocytic compartmen ts appeared to be decreased in the mutant. Endocytosed tracer moved mo re rapidly to the cell poles in FD1.3.25 than in wild type cells, An a bundant 36-kD polypeptide was found associated with taxol-polymerized microtubules in preparations from wild type and mutant; in the former but not the latter this polypeptide could be dissociated by incubation of the microtubules in ATP or high salt. The 36-kD polypeptide co-ele ctrophoresed in two dimensions with the monomer of the glycolytic enzy me glyceraldehyde 3-phosphate dehydrogenase (GAPDH). Analysis of cDNA clones showed that the mutant is heterozygous for this enzyme, with si milar to 25% of the GAPDH RNA containing a single nucleotide change re sulting in substitution of Ser for Pro(234), a residue that is conserv ed throughout evolution. Stable transfectants of wild type cells expre ssing the mutant monomer at similar to 15% of the total enzyme exhibit ed the various changes in endocytosis observed in FD1.3.25.