Pre-60S ribosome synthesis S Granneman et al cally interact in early pre-60S particles: Brx1, Cic1/Nsa3, Erb1, Ebp2, Nop4, Nop7, Nop12, Nop15, Pwp1 and Ytm1 (see Figure 1B for interaction map). Except for Rlp7 and Ebp2, all of these factors were tested in CRAC analyses, and six (Cic1, Erb1, Nop4, Nop7, Nop12 and Nop15) efﬁciently crosslinked to RNA. The locations of crosslinking sites along the rDNA are indicated in Figure 3A and C, and are displayed on the predicted secondary structures of 25S, 5.8S and ITS2 in Figure 3D. CRAC experi- ments were performed 2–5 times and to be considered a bona ﬁde RNA binding site, a nucleotide sequence had to be signiﬁcantly enriched in every experiment. As negative con- 4008 The EMBO Journal VOL 30 | NO 19 | 2011 & 2011 European Molecular Biology Organization