Figure 5.

Depletion of L17 or L37 leads to a defect in processing of 27SB pre-rRNA and its eventual turnover. (A) Synthesis and turnover of pre-rRNAs were assayed by pulse-chase experiments. GAL-HA-RPL17 and pGAL-RPL37 cells were grown in galactose- or glucose-containing medium lacking methionine for 16–17 h. Cells were pulse-labeled with [³H-methyl]-methionine for 5 min and chased with an excess of nonradioactive methionine. Total RNA was extracted, and equal numbers of radioactive counts were loaded onto denaturing agarose gels, transferred to nitrocellulose membranes, and exposed to X-ray films. (B) Total RNA was extracted from GAL-HA-RPL17 and pGAL-RPL37 strains grown in galactose or shifted to glucose for 16–17 h at 30°C. Samples were subjected to primer extension analysis of 5′-ends of 27S and 7S pre-rRNAs. The asterisk indicates 5′-truncated pre-rRNAs formed specifically in the absence of L17. (C) Total RNA was extracted as described earlier, and 7S pre-rRNAs were assayed by northern hybridization. U2 was probed to serve as a loading control.