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

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Ribonucleoprotein complexes of Drosophila melanogaster Kc tissue culture cells grown at 24°C or heat-shocked at 37°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°C and 37°C culture cells possess buoyant densities in CsCI between ϱ = 1.38 g/cm-3 and 1.43 g/cm-3. The 35S-labelled proteins bound to the hnRNA of 37°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°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.

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