Ria1p (Ynl163c), a protein similar to elongation factors 2, is involved inthe biogenesis of the 60S subunit of the ribosome in Saccharomyces cerevisiae

RIA1 (YNL163c) is a quasi-essential gene that encodes a protein with strong similarities to elongation factors 21. Small C-terminal deletions in the p rotein lead to a severe growth defect. In the case of a 22-residue C-termin al deletion this can be suppressed by intragenic mutations in the RIA1 gene or dominant extragenic mutations in TIF6, which is thought to be involved in the biogenesis of the 60S subunit of the ribosome. The dominant TIF6 all eles can also suppress the phenotype associated with a complete deletion of the RIA1 gene. Depletion of Ria1p has a dramatic effect on the polysome pr ofile: there is a severe reduction in the level of the 80S monosomes, an im balance in the 40S/60S ratio, and halfmers appear. Dissociation of the mono somes and polysomes in the Ria1p depletion mutant revealed a specific reduc tion in the amount of 60S subunits. Localization experiments with HA-tagged derivatives of Ria1p did not detect any stable association of Ria1p with r ibosome subunits, 80S monosomes or polysomes. Cell fractionation experiment s show that Ria1p is found in both the cytoplasmic fraction and the nuclear fraction. Taken together, these data suggest that Ria1p is involved in the biogenesis of the 60S subunit of the ribosome.