The research of this laboratory involves analysis of complex cellular pathways through biochemical genetics. The primary defect in FD1.3.25, a Chinese hamster ovary (CHO) cell mutant exhibiting genetically dominant aberrations in endocytosis and secretion, appears to reflect a single nucleotide substitution in one of the two alleles encoding the glycolytic enzyme glyceraldehyde 3-phosphate dehydrogenase. The mutant polypeptide was originally identified on the basis of its persistent association with microtubule preparations, also shown to be a genetically dominant trait; this correlates with the abnormal association of both late endosomes and secretory vesicles with microtubules observed in FD1.3.25. Studies directed toward elucidation of the interactions among microtubules, vesicles and the mutant polypeptide have been initiated. CHB11.1.3, isolated in this laboratory, like other CHO cell mutants utilizing polyprenol rather than dolichol in lipid-dependent N-linked glycosylation reactions, shows its greatest deficit with respect to synthesis of the nonamannosyl oligosaccharide. Recent results may prove significant in uncovering the relationship between the structure of the lipid and the nature of the oligosaccharide synthesized. First, it has been shown in CHB11.1.3 and two independent dolichol mutants supplied by others, that the synthesis of nonamannosyl oligosaccharide is restored by shifting the cells to 0 degrees. Second, a phenotypic revertant of CHB11.1.3, RR1.3.4, is the only one described to date exhibiting restoration of dolichol synthesis; RR1.3.4 accomplishes this through overproduction of polyprenol.
