Defective processing of ribosomal precursor RNA in Saccharomyces cerevisiae

Saccharomyces cerevisiae (strain A224A) has an abnormal distribution of cytoplasmic ribosomal subunits when grown at 36 degrees C, with sucrose-gradient analysis of extracts revealing an apparent excess of material sedimenting at 60 S. This abnormality is not observed at either 23 degrees C or 30 degrees C. At 36 degrees C the defect(s) is expressed as a slowed conversion of 20 S ribosomal precursor RNA to mature 18 S rRNA, although the corresponding maturation of 27 S ribosomal precursor RNA to mature 25 S rRNA is normal. Studies on this yeast strain and on mutants derived from it may help to elucidate the role(s) of individual ribosomal components in controlling ribosome biogenesis in eukaryotes.