The Mak11 homologue in S. pombe, Skb15, is involved in 60S formation in fission yeast. (A and B) Cells expressing SKB15 under the control of the nmt1 thiamine-repressible promoter were grown in synthetic medium without thiamine (A) or with 5 μg/ml thiamine (B). Extracts were separated by sucrose gradient ultracentrifugation, and the amounts of free 40S, free 60S, and polysomes were estimated by the 254-nm absorbance profile. (C) A wild-type S. pombe strain and a strain expressing Skb15-TAP were used for the first step of TAP; RNAs were extracted with phenol-chloroform and tested by Northern blotting or primer extension with oligonucleotides specific for pre-rRNAs or U2 as control.