UBF is essential for the synthesis of the major rRNAs in cell culture.

<p>A) to E) <i>Ubf^fl/fl/Er-cre^+/+</i> and <i>Ubf^wt/wt Er-cre^+/+</i> cells were treated with 4-HT to induce recombination in the <i>Ubf</i> gene and at the indicated time points, A) genotyped for <i>Ubf</i> recombination, B) analyzed by Western blot for UBF levels, and C) metabolically labelled with [³H]-uridine to follow rRNA synthesis of the rRNAs and their precursors. D) Northern blot analysis of the 47S and 34S rRNA pools. The upper diagram shows the organisation of the larger rRNA precursors and the probe used. In C) “Bulk” refers to the EtBr stained total RNA fractionation. E) Quantitative analyses of rRNA synthesis rates and pool sizes.