Molecular analysis of alpha ecdysone induced 16S complexes in Drosophila Schneider's S3 cells

The molecular organization of alpha ecdysone induced small heat shock proteins (small hsps) in Schneider's S3 tissue culture cells was analysed. Sucrose gradient centrifugation of cytoplasmic extracts and nondenaturing gel electrophoresis shows that hormone induced small hsps form 16S particles which differ in the relative molar ratios of the small hsps composing the 16S particles. The 16S particles possess a buoyant density in Cs2SO4 of rho = 1.34 g/cm3 which is indicative of RNP complexes with an RNA:protein ratio of 1:4. The RNA component of the 16S particles was identified by cDNA cloning using a cDNA library established from alpha ecdysone induced pupal 16S material. Northern hybridization using the 16S RNP specific partial cDNA clone Ec3 identifies a single alpha ecdysone inducible 300 nt RNA species. Our data suggest that the small hsps may unfold their so far unresolved function in form of RNP complexes.