Posttranslational modification of elongation factor 2 in diphtheria-toxin-resistant mutants of CHO-K1 cells.
We have identified two types of mutants of Chinese hamster ovary cells in which the unique ADP-ribose attachment site in elongation factor 2 (EF-2) is altered, thereby rendering them resistant to diphtheria and Pseudomonas toxins (TOXR). The first is mutant in the gene for EF-2 and possesses a permanently altered, TOXR gene product. The second lacks a component of a posttranslational modification system that converts TOXR EF-2 to the toxin-sensitive (TOXS) state. We postulate that this modification system is involved in the conversion of a single histidine residue in EF-2 to the specific target of toxin-catalyzed ADP-ribosylation, the novel amino acid X. We have designated the second type MOD- mutants. The missing of nonfunctional component in the MOD- mutants can be restored by hybridizing them with either normal TOXS cells or with EF-2 structural gene mutants. The TOXR EF-2 from MOD- mutants is also converted to toxin sensitivity in vitro by incubation with extracts of TOXS or EF-2 gene mutant cells in the presence of an energy-generating system. Our results demonstrate that EF-2 can be synthesized and released from ribosomes in a toxin-resistant form and then converted to toxin sensitivity by posttranslational modification.
D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D002474:Cell-Free System; D006224:Cricetinae; D004167:Diphtheria Toxin / Q000494:pharmacology*; D004351:Drug Resistance; D006822:Hybrid Cells / Q000187:drug effects; D009154:Mutation; D010445:Peptide Elongation Factors / Q000235:genetics / Q000378:metabolism*; D014176:Protein Biosynthesis
D004167:Diphtheria Toxin; D010445:Peptide Elongation Factors; D000246:Adenosine Diphosphate Ribose