Fig. 2. Incorporation of SRP RNA into amplified nucleoli. Recombinant human SRP RNA (A-C) and control RNA antisense to canine SRP RNA (D-F) were labelled with Alexa 488 and injected into the GVs of Xenopus oocytes. After 18 hours, GVs were isolated and spread preparations were counterstained with DAPI. Fields containing nucleoli (No) were located by phase-contrast microscopy (A,D) and generally also contained chromosomes (Ch), Cajal bodies (CB) and B-snurposomes (smaller particles throughout the field). DNA-rich regions of chromosomes (chromomeres) and nucleoli (fibrillar centres) were located by DAPI fluorescence (B,E) and injected RNA was located by Alexa 488 fluorescence (C,F). SRP RNA was targeted specifically to nucleoli (C), whereas control antisense RNA failed to concentrate in any nuclear structures (F), although autofluorescence is seen from a contaminating yolk platelet (YP).