A biochemical and ultrastructural study of RNA in yolk platelets of Xenopus gastrulae.

Yolk platelets from Xenopus gastrulae were isolated in a sucrose-polyvinyl pyrrolidone medium, washed, centrifuged four times, and portions of each pellet were prepared for electron microscopy. Electron microscopy revealed isolated platelets to be free of cytoplasmic contamination with progressive disruption of the superficial layer after each washing. Each washing and the final pellet were extracted with phenol and precipitated with ethanol. Orcinol analysis indicated that 50-60 fig of RNA were present in yolk platelets isolated from 1000 gastrulae. Autoradiography of yolk platelets from cells incubated in [5-H]uridine revealed label in superficial and main body components after treatment with DNase but not after incubation in RNase. Acrylamide-gel electrophoresis suggests that yolk platelet RNA is of both high and low molecular weight.