Heat-shock puff 93 D from Drosophila melanogaster: accumulation of a RNP-specific antigen associated with giant particles of possible storage function.

The monoclonal antibody P11 is directed against a 38 000 dalton protein of Drosophila melanogaster. On polytene chromosomes this protein is present in a subset of the RNA polymerase II-containing loci. Here we show by density centrifugation and enzyme-linked immunosorbent assay tests that the P11 antigen is part of nuclear ribonucleoprotein (RNP) complexes. Indirect immunofluorescence shows that, after prolonged heat-shock, the P11 antigen is present only in the heat-shock puff 93 D. Identical distribution patterns were obtained with another monoclonal antibody, Q18. Unlike P11, this antibody also cross-reacts with D. hydei and D. virilis polytene chromosomes, where the puffs 48 B and 20 CD, respectively, are the only loci prominently stained after heat-shock. The small and giant RNP complexes previously described in these puffs were also observed in puff 93 D. Both types of particle contain the P11 antigen as shown by immunoelectron microscopy. We suggest that the P11 antigen is associated with a special class of RNPs which are possibly involved in the storage of primary transcription products inside the nucleus.