Figure 7.

Function of Rps2 in fission yeast pre-rRNA processing. Our results indicate that Rps2 is required for efficient processing at site A2. In conditions of Rps2 insufficiency, the 32S precursor is cleaved at site A3, as suggested by the detection of 21S rRNA precursors. The kinetics of pre-rRNA accumulation as determined by pulse-chase assays suggest that most 40S precursors are rapidly degraded in the absence of Rps2. Whether 21S- or 20S-containing particles, or both, are subject to this rapid turnover remains to be determined. The remaining 20S-containing small subunit precursors are not processed into mature 18S rRNA in the cytoplasm because they are retained in the nucleolus.