Bop1Δ inhibits processing of the 36S and 32S precursors to form the 28S rRNA. Clonal LAP3 cell lines transfected with either the empty pX11 vector (line 1-1), pX11-Bop1 (line 45), or pX11-Bop1Δ (line 6) were either left untreated (−) or treated with 1 mM IPTG for 16 h (+) and pulse-labeled with 3H-labeled methyl methionine for 30 min. After a chase in nonradioactive medium plus excess methionine for the indicated times, RNA was isolated, resolved on a 1% agarose gel, transferred to a membrane, and visualized by fluorography.