Figure 1.

CBs in a HeLa cell nucleus. (A) DIC image showing four prominent nucleoli and three faintly detectable CBs (arrowheads). (B) The same nucleus immunostained with antibodies against coilin (green) and fibrillarin (red). The three CBs in this nucleus appear yellow because they stain with both antibodies. The nucleoli stain only for fibrillarin. Fibrillarin is the methyltransferase for 2′-O-methylation of rRNA in the nucleoli and snRNAs in the CBs. Modified from Gall (2003) with permission from Nature Reviews. Bar = 10 µm.