Fig. 4. Immunogold detection of BrUTP-labelled rRNAs on ultrathin sections of isolated nucleoli from ELT cells pulse-labelled for 10 minutes with BrUTP and pulse-labelled for 10 minutes with BrUTP followed by a 20 minute chase with UTP. Densities (gold particles/µm²) on the FC, DFC, GC and resin (R) were calculated in both cases. The results shown represent means±s.e.m. 13 and 25 random micrographs were analyzed, and 306 and 420 gold particles were counted, respectively. Student's t-test for nucleolar components versus resin (+ P<0.05, ++ P<0.01) for each nucleolar component in pulse-labelled versus pulse-labelled and chased nucleoli (^* P<0.05, ^** P<0.01) and for FC versus DFC in pulse-labelled or pulse-labelled and chased nucleoli (^ P<0.05, ^^ P<0.01) was used.