A lethal mutation which affects the maturation of ribosomes

Summary Among a group of 31 ts^- yeast mutants screened electrophoretically for heat-sensitive synthesis of each stable RNA species, only mutant ts351 failed to accumulate 25S RNA at 36°C. Pulse-labeling experiments at 36°C showed that 35S and 27S precursor RNA and mature 18S r-RNA molecules are synthesized by ts351 cells but that 25S and 5.8S RNA species are not made and new 60S ribosomal sub-units are not assembled. The mutant is blocked at a specific point in r-RNA processing: the cutting of 27S to form 25S and 5.8S r-RNA.