Abstract
Chinese hamster ovary cell mutants resistant to the translational inhibitor emetine (Emt B mutants) express a single genetically altered 40S ribosomal subunit protein, S14. that appears to account for their drug resistance. To determine whether Emt B mutation affect the structural gene for the S14 protein, we isolated mRNAs from several wild-type and Emt B mutant clones. We translated the mRNAs in a cell-free system derived from wheat germ, and we discerned the biosynthesis of 59 ribosomal proteins, including S14. In every case, poly(A)+ mRNA programmed the cell-free system to synthesize an S14 protein electrophoretically identical to the S14 extracted from the ribosomes of the corresponding cell line. Messages from two Emt B mutants (Emr-2 and Emr-2-2) specified S14s that were electrophoretically distinct from the wild-type protein. Thus, Emt B mutations were expressed in mutant cell mRNAs, apparently reflecting mutagen-induced changes in S14 structural genes.