title: Relationship between histidyl-tRNA level and protein synthesis rate in wild-type and mutant Chinese hamster ovary cells.
abstract: A preliminary investigation was carried out to determine how conditional lethal mutants affected in particular aminoacyl-tRNA synthetases may be used to study the role of tRNA charging levels in protein synthesis. The relationship between rate of protein synthesis and level of histidyl-tRNA in wild-type cultured Chinese hamster ovary cells was determined using the analogue histidinol to inhibit histidyl-tRNA synthetase activity. This response was compared with that obtained using a mutant strain with a defective histidyl-tRNA synthetase that phenotypically shows decreased rates of protein synthesis at reduced concentrations of histidine in the growth medium. The approach used was based on measuring the histidyl-tRNA levels in live cells. The percentage charging was estimated by comparing [14C]histidine incorporated into alkali-labile material in paired samples, one of which was treated with cycloheximide, five minutes before terminating during the incubation, to produce maximal aminoacylation. Wild-type cells under histidinol inhibition exhibited a sensitive, sigmoidal relationship between the level of histidyl-tRNA and the rate of protein synthesis. A decrease in the relative percentage of acylated tRNA (His) from 46% to 35% elicited a large reduction in the rate of protein synthesis from 90% to 30% relative to untreated cells. An unpredicted result was that the relationship between protein synthesis and histidyl-tRNA in the mutant was essentially linear. High acylation values for tRNA (His) were associated with rates of protein synthesis that were not nearly as high as in wild-type cells. These findings suggest that the charging charging levels of tRNA (His) isoacceptors could play a regulatory role in determining the rate of protein synthesis under conditions of histidine starvation in normal cells. The mutant appears to be a potentially useful system for studying the pivotal role of tRNA charging in protein synthesis, assuming that the altered response in the mutant is caused by its altered synthetase.
mesh_terms: D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D003513:Cycloheximide / Q000494:pharmacology; D005260:Female; D006639:Histidine / Q000378:metabolism*; D007700:Kinetics; D009154:Mutation; D010053:Ovary; D014176:Protein Biosynthesis / Q000187:drug effects; D012343:RNA, Transfer / Q000378:metabolism*; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism*
chemical_list: D012346:RNA, Transfer, Amino Acyl; D006639:Histidine; D012343:RNA, Transfer; D003513:Cycloheximide