Genetic and biochemical analysis of mutation(s) affecting ricin internalization in Chinese hamster ovary cells

We have previously reported the isolation and characterization of Chinese hamster ovary (CHO) cell mutants defective in the internalization of ricin (Ray, B., and Wu, H.C. (1982) Mol. Cell. Biol. 2, 535-544). These mutants also do not exhibit the enhancement of ricin internalization by nigericin pretreatment at a low concentration, which is observed in the wild-type CHO cells. An analysis of somatic cell hybrids between the mutant and the toxin-sensitive wild-type CHO cell line shows that all of the phenotypes associated with the toxin resistance mutation are dominant in the hybrid cell lines. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of [3H]palmitic acid-labeled cell extracts from the mutant and toxin-resistant hybrid cell lines has revealed an increased incorporation of [3H] palmitic acid into two proteins with apparent molecular weights near 30,000 in the mutant and hybrid cells as compared to that in the wild-type cell line. Our studies indicate that these two fatty acyl proteins might be related to a dominant mutation(s) which results in a decreased uptake of ricin.