Small ribonucleic acid molecules produced during ribosome biosynthesis in Saccharomyces cerevisiae

A 5.8 S ribosomal RNA (rRNA) is found noncovalently bound to the 25 S RNA in the 60 S subunit of yeast ribosomes. Both molecules appear to be derived from the 27 S RNA, a ribosomal precursor species (Uden, S. A., and Warner, J. R. (1972) J. Mol. biol. 65, 227-242). We have detected two other RNA species by pulse labeling which may also be produced during 27 S RNA processing. The first is approximately 5.9 S and appears by kinetics of synthesis to be a direct precursor of 5.8 S rRNA. The second species is about 7 S, is absent from uniformly labeled RNA preparations, and is produced coincidentally with the 5.8 S rRNA. Both the 5.9 S RNA and the 7 S RNA are not produced in mutants defective in ribosome biosynthesis (Hartwell, L. H., McLaughlin, C. S., and Warner, J. R. (1970) Mol. Gen. Genet. 109, 42-56) which are unable to make the 25 S-5.8 S rRNA complex from 27 S RNA. Thus, the maturation of 27 S RNA appears to involve the production of a 7 S RNA, which could be either a precursor or a nonconserved RNA region, and a 5.9 S RNA, most of which is trimmed to give the mature 5.8 S rRNA in the 25 S-5.8 S rRNA complex of 60 S subunits.