Heat-shock proteins are associated with hnRNA in Drosophila melanogaster tissue culture cells

Abstract

Ribonucleoprotein complexes of Drosophila melanogaster Kc tissue culture cells grown at 24 degrees C or heat-shocked at 37 degrees C were cross-linked in vivo by u.v. irradiation. Cross-linked heterogeneous nuclear ribonucleoprotein (hnRNP) complexes were fractionated by oligo(dT)-cellulose chromatography and CsCI density centrifugation. The hnRNP complexes of both 24 degrees C and 37 degrees C culture cells possess buoyant densities in CsCI between varrho = 1.38 g/cm and 1.43 g/cm. The S-labelled proteins bound to the hnRNA of 37 degrees C culture cells correspond in mol. wt. to the so-called heat-shock proteins of 70 K, 68 K, 27 K, 26 K, 23 K and 22 K. The 70 K and 68 K proteins are also present in hnRNP complexes of 24 degrees C culture cells. In addition, several other Drosophila hnRNPs of 140 K, 56 K, 45 K, 43 K, 38 K, 37 K and 34 K, whose synthesis is strongly repressed under heat-shock conditions, could be identified. The results demonstrate that the so-called heat-shock proteins possess a function as RNPs.