Saccharomyces cerevisiae mutants defective in the maturation of ribosomal RNA.

Slow-growing mutants were isolated after mutagenesis of the osmotic-sensitive strain Saccharomyces cerevisiae VY1160. The isolated mutants in rich media have generation times from 300 to 400 min at 30 degrees C. Studies on the biosynthesis of rRNAX have shown, that the processing of 37S pre-rRNA in 6 of the slow-growing mutants occurs 3 to 4 times slower than in the parental strain. These mutants with decreased rate of rRNA maturation are of two different types. In some of them the processing of both 37S and 27S pre-rRNA is slowed down, while the mutants from the second group are acharacterized by a specific inhibition of the step 27S pre-rRNA leads to 25S rRNA. Experiments in which the synthesis of macromolecules was studied, have shown that in the mutants and in the parental strain, RNA and proteins are synthesized at comparable rates. Preliminary results suggest that the decreased rate of rRNA processing in three of the isolated mutants might be due to an insufficient function of the enzymes involved in the maturation of rRNA.