Isolation and characterization of nuclear ribonucleoprotein complexes from Drosophila melanogaster

Transcription of heat shock gene loci versus non-heat shock loci in Chironomus polytene chromosomes: evidence for heat-induced formation of novel putative ribonucleoprotein particles (hsRNPs) in the major heat shock puffs

The heat shock response of Chironomus polytene chromosomes was reexamined. The in vivo effects of heat shock on chromosomal [3H]uridine labeling, RNA polymerase II distribution and ribonucleoprotein (RNP) formation were investigated. One primary result is a clarification of the number and location of chromosomal sites strongly induced by treatment at 37 degrees C for 60 min. In total, seven major heat shock loci were identified by transcription autoradiography in Chironomus tentans: I-20A, II-16B, II-10C, II-4B, II-1C, III-12B, and IV-5C. Secondly, combining immunofluorescence with transcription autoradiography, I find RNA polymerase II occurring after heat shock at multiple chromosomal sites that were also active under normal conditions (20 degrees C). Furthermore, the results demonstrate conclusively that the presence of RNA polymerase II at heat shock and non-heat shock loci is generally correlated with [3H]uridine labeling during heat shock. These latter results extend and corroborate previous findings. Thirdly, the most striking result of this study was revealed in ultrathin sections of puffs by electron microscopy: I discerned a site-specific ultrastructural difference in putative RNP particles between heat shock versus non-heat shock loci. At least three of the seven induced major heat shock puffs (I-20A, III-12B, IV-5C) were observed to contain globular particles that were different, i.e. significantly larger, 250-1,000 A in diameter with a prominent 500-750 A class, than RNP particles of other loci under non-heat shock conditions. These large heat shock puff particles presumably represent nascent or newly synthesized heat shock RNA associated with protein(s) to form heat shock RNPs (hsRNPs). This finding suggests the possible involvement of novel RNPs (hsRNPs) in transcriptional regulation or heat shock RNA turnover and may stimulate further molecular investigations on this subject in both cell physiological and structural terms. I conclude that the locus-specific putative hsRNPs are an intrinsic property of greatly increased heat shock gene transcription.

Isolation of hnRNP complexes from Drosophila melanogaster

Nascent RNA polymerase II transcripts, heterogeneous nuclear RNAs (hnRNAs), become associated with nuclear proteins (hnRNP Proteins), and their processing into mRNAs takes place in these hnRNP complexes. hnRNP complexes have previously been purified from vertebrate cells. Here we report the isolation of hnRNP complexes from an invertebrate organism, the fruitfly Drosophila melanogaster. Candidate hnRNP proteins were purified from D. melanogaster embryos by ssDNA affinity chromatography, and mAbs were produced to many of the major proteins. Genuine hnRNP proteins were identified by several criteria, including nucleoplasmic localization, association with nascent transcripts, crosslinking to poly(A)-containing RNA in living cells, and amino acid sequence. In addition, mAbs that cross-react between the fruitfly and human hnRNP proteins were obtained. Most importantly, using hnRNP-specific mAbs we have purified the hnRNP complexes from D. melanogaster cells. These RNAase-sensitive complexes contain at least 10 major proteins designated hrps, the most abundant proteins having apparent molecular masses of 36, 38, 39, 40, 44, 48, 54, 62, 70, and 75 kD. cDNAs and complete sequences for several of these proteins have been obtained and are presented in the accompanying paper (Matunis, E. L., M. J. Matunis, and G. Dreyfuss. 1992. J. Cell Biol. 116:257-269). The purification of D. melanogaster hnRNP complexes will facilitate genetic and cytological studies on the function of hnRNA-binding proteins and on the posttranscriptional regulation of gene expression.

Nonpackaging and packaging proteins of hnRNA in Drosophila melanogaster

Monoclonal antibodies have previously been raised against chromosomal proteins of Drosophila. Using a biochemical fractionation method for the isolation of large hnRNA-containing structures (hnRNP) of Drosophila tissue culture cells, we show that seven of these antibodies recognize different antigens, and that these antigens are associated with RNA. Analysis of the sedimentation behavior of antigen-containing structures in sucrose gradients reveals that the antigens are differentially distributed with respect both to one another and to pulse-labeled RNA. We demonstrate that the antigens are minor components of hnRNP and are different from the major Drosophila hnRNP packaging proteins, which we have also identified. The antigens are probably involved in the processing of hnRNA in the nucleus.