Characterization of a poly(A)+RNA-containing structural component directly associated with cytoplasmic membranes in...

Poly(A)+RNA-containing material was extracted from the purified cytoplasmic membranes of dormant Artemia cysts by treatment with mild detergents. Sedimentation analysis of the extracts showed a predominant poly(A)-containing fraction at 40 S, associated with about 6% of the extracted proteins. Only limited amounts of poly(A)-containing material were found in the heavier fractions. Poly(A)+RNA extracted from the 40-S fraction sedimented around 14 S. The poly(A)-containing 40-S structures could be purified by treatment with non-ionic or zwitterionic detergents followed by resedimentation in sucrose gradients in the presence or absence of detergent. When the 40-S fraction was analyzed by isopycnic centrifugation in Cs2SO4 gradients, the main part of the poly(A)-containing material banded at a density of 1.27 g/ml. Electron-microscopic examination of this fraction revealed circular or slightly bullet-shaped profiles measuring 17-26 nm. When the 40-S fraction had been submitted to mild RNAase treatment prior to density gradient centrifugation, the material was displaced towards lower density and became less distinct. Purified 40-S particles showed a complex protein pattern not very similar to that of polyribosomal poly(A)+RNA-containing particles from developing embryos, but with components in common with unfractionated membranes. The particles also contained some lipids. The experiments indicate that a major part of the membrane-bound, latent poly(A)+RNA in dormant Artemia cysts occurs in the form of relatively uniform, detergent- and Cs2SO4-resistant structures, independent of ribosomes, but intimately associated with membrane components.