Heterogeneous nuclear ribonucleoprotein complexes and proteins in Drosophila melanogaster.

Pre-mRNAs cotranscriptionally associate with a small group of proteins to form heterogeneous nuclear ribonucleoprotein (hnRNP) complexes. We have previously identified two genes in Drosophila melanogaster, Hrb98DE and Hrb87F (i.e., genes at 98DE and 87F encoding putative hnRNA binding proteins), which encode five protein species homologous to the mammalian A-B hnRNP proteins. The studies presented herein show that antibodies against the RNP domains of Hrb98DE reacted with 10 to 15 distinct spots of 38 to 40 kDa in the basic region of two-dimensional gels. These nuclear proteins bound single-stranded nucleic acids and were extracted from Drosophila tissue culture cells as 40 to 80S hnRNP complexes in association with 300 to 800 nucleotide fragments of RNA. The peak of poly(A)+ RNA sequences was coincident with the peak of HRB proteins in sucrose gradients, strongly suggesting that the HRB complexes identified are Drosophila hnRNP complexes. The repertoire of HRB proteins did not change significantly during embryogenesis and was similar to that observed in Drosophila tissue culture cells. Analyses with peptide-specific antisera demonstrated that the major proteins in the hnRNP complex were encoded by the two genes previously identified. Although the Drosophila HRB proteins are only approximately 60% identical throughout the RNP domains to the mammalian A-B hnRNP proteins, features of the basic pre-mRNA packaging mechanism appear to be highly conserved between D. melanogaster and mammals.

The Drosophila Hrb98DE locus encodes four protein isoforms homologous to the A1 protein of mammalian heterogeneous nuclear ribonucleoprotein complexes.

The Drosophila Hrb98DE locus encodes proteins that are highly homologous to the mammalian A1 protein, a major component of heterogeneous nuclear ribonucleoprotein (RNP) particles. The Hrb98DE locus is transcribed throughout development, with the highest transcript levels found in ovaries, early embryos, and pupae. Eight different transcripts are produced by the use of combinations of alternative promoters, exons, and splice acceptor sites; the various species are not all equally abundant. The 3'-most exon is unusual in that it is completely noncoding. These transcripts can potentially generate four protein isoforms that differ in their N-terminal 16 to 21 amino acids but are identical in the remainder of the protein, including the RNP consensus motif domain and the glycine-rich domain characteristic of the mammalian A1 protein. We suggest that these sequence differences could affect the affinities of the proteins for RNA or other protein components of heterogeneous nuclear RNP complexes, leading to differences in function.

A unique ribonucleoprotein complex assembles preferentially on ecdysone-responsive sites in Drosophila melanogaster.

The protein on ecdysone puffs (PEP) is associated preferentially with active ecdysone-inducible puffs on Drosophila polytene chromosomes and contains sequence motifs characteristic of transcription factors and RNA-binding proteins (S. A. Amero, S. C. R. Elgin, and A. L. Beyer, Genes Dev. 5:188-200, 1991). PEP is associated with RNA in vivo, as demonstrated here by the sensitivity of PEP-specific chromosomal immunostaining in situ to RNase digestion and by the immunopurification of PEP in Drosophila cell extract with heterogeneous nuclear ribonucleoprotein (hnRNP) complexes. As revealed by sequential immunostaining, PEP is found on a subset of chromosomal sites bound by the HRB (heterogeneous nuclear RNA-binding) proteins, which are basic Drosophila hnRNPs. These observations lead us to suggest that a unique, PEP-containing hnRNP complex assembles preferentially on the transcripts of ecdysone-regulated genes in Drosophila melanogaster presumably to expedite the transcription and/or processing of these transcripts.

Human IgG1 and its Fc fragment bind with different affinities to the Fc receptors on the human U937, HL-60 and ML-1 cell lines.

Measurements were made of the binding of human monomeric 125I-IgG1 and 125I-Fc to U937 cells at room temp. Analyses of the binding data showed that these cells possessed a single class of receptor (FcR) for Fc or IgG and, although both ligands were found to bind to the same number of sites per cell, Fc was found to bind with about twice the affinity of IgG. At 20 degrees C estimates of the forward rate constants and the dissociation rate constants for IgG and Fe were 1.13 and 3.65 X 10(7) M-1 min-1 and 0.33 and 0.57 X 10(-2) min-1 respectively. Independent determinations of the association constants (Ka) under the same experimental conditions gave values of 0.98 X 10(9) M-1 for IgG and 3.1 X 10(9) M-1 for Fc. Thus the Fc fragment of IgG appears to bind to U937 FcR at 3-4 times the rate of IgG and to dissociate at about twice the rate, resulting in higher values of Ka for the Fc-FcR than for the IgG-FcR interaction. Also, in competitive-binding experiments and in EA rosette inhibition assay the Fc fragment was consistently found to be more efficient in FcR binding than IgG. Similar results were obtained using HL-60 and ML-1 cells which possess FcR like those on U937 cells and with IgG1 and Fc prepared from other myelomas. IgG and Fe which had undergone mild reduction and alkylation bound to the same number of FcR per U937 cell as the non-reduced ligands but the affinity of binding was diminished to a similar degree with both ligands, suggesting that the major effect of cleavage of the interchain disulfide bonds on cytophilic binding is due to alteration of the native quaternary relationships of the C gamma 2 and C gamma 3 domains.

Prevention of adrenocortical hyperactivity by dietary casein in rats exposed to forced swimming stress.

Adrenal weight, adrenal hydroxysteroid dehydrogenase activity and serum corticosterone level were significantly higher in rats fed with 5% casein diet after 7 days of swimming stress (45 min/day) as compared to their controls. All the parameters were similar to their control levels in rats receiving 20% casein diet and exposed to swimming stress. The results suggest that casein can play an important role in preventing adrenocortical hyperactivity in swimming stressed rats.

The Drosophila Hrb87F gene encodes a new member of the A and B hnRNP protein group.

Nascent premessenger RNA transcripts are packaged into heterogeneous nuclear ribonucleoprotein (hnRNP) complexes containing specific nuclear proteins, the hnRNP proteins. The A and B group proteins constitute a major class of small basic proteins found in mammalian hnRNP complexes. We have previously characterized the Drosophila melanogaster Hrb98DE gene, which is alternatively spliced to encode four protein isoforms closely related to the A and B proteins. We report here that the Drosophila genome contains a family of genes related to the Hrb98DE gene. One member of the family, Hrb87F, is very homologous to Hrb98DE in both sequence and structure. The Hrb87F transcripts (1.7 and 2.2 kb) utilize two alternative polyadenylation sites, are abundant in ovaries and early embryos, and are present in lesser amounts throughout development. In one wildtype strain of Drosophila there is a naturally-occurring polymorphism in this gene due to the insertion of a 412 transposable element in the 3' untranslated region. The larger transcript is not produced in these files and thus is not required for viability. Sequence identities among the Drosophila Hrb proteins and the vertebrate A and B hnRNP proteins suggest that these proteins may form a distinct subfamily within the larger family of related RNA binding proteins.

An investigation into the role of coagulation factor XIII in ADP-induced aggregation and fibrinogen binding with rabbit platelets.

Because there was a possibility that activated factor XIII (factor XIIIa) might stabilize a platelet-fibrinogen aggregate through its crosslinking action, we have isolated plasma factor XIII, activated it, and studied the effect of factor XIIIa at a concentration of 3.3 micrograms/ml on aggregation and 125I-fibrinogen binding of rabbit platelets stimulated with 9 microM ADP. Factor XIIIa did not cause aggregation in the absence of ADP, nor did it enhance ADP-induced aggregation or substantially stabilize the platelet aggregate. The presence of factor XIIIa did not affect the amount of fibrinogen bound to platelets immediately after stimulation with ADP, but it appeared to cause a slow specific binding of 125I-fibrinogen to platelets whether or not they were stimulated with ADP. This binding, which was not inhibited by prostaglandin E1, did not lead to aggregation and was accompanied by crosslinking of fibrinogen through its A alpha and gamma chains, either to other fibrinogen molecules or to a platelet protein or proteins.

Utilization of chimeras between human (HM-175) and simian (AGM-27) strains of hepatitis A virus to study the molecular basis of virulence.

Chimeras between human (HM-175) and simian (AGM-27) strains of hepatitis A virus (HAV) were constructed to evaluate the effect of the 2C gene of AGM-27 on HAV replication in cell culture and virulence in tamarins (Saguinus mystax) and chimpanzees (Pan troglodytes). Kinetic studies and radioimmunofocus assays demonstrated that replacement of the 2C gene of HAV/7, a cell culture-adapted strain of HM-175, with that of AGM-27 drastically reduced the ability of the virus to replicate in cultured cells. Intragenic chimeras containing AGM-27 sequences in either the 5' or 3' half of the 2C gene replicated in cell culture at an intermediate level. Whereas HAV/7 is attenuated for tamarins, a chimera containing the simian virus 2C gene in the HAV/7 background was virulent in tamarins, demonstrating that the simian virus 2C gene alone can confer the phenotype of virulence to an otherwise attenuated virus. Clusters of AGM-27-specific residues near both ends of the 2C protein were required for virulence since a chimera containing AGM-27 sequences in the carboxy-terminal half of 2C was partially attenuated for tamarins while one containing AGM-27 sequences only in the amino-terminal half of 2C was even more attenuated. Chimeras containing either the entire or only the 3' half of the simian virus 2C gene in the HAV/7 background were attenuated for chimpanzees.

Progress toward the development of a genetically engineered attenuated hepatitis A virus vaccine.

Mutations which positively affect growth of hepatitis A virus in cell culture may negatively affect growth in vivo. Therefore, development of an attenuated vaccine for hepatitis A may require a careful balancing of mutations to produce a virus that will grow efficiently in cells suitable for vaccine production and still maintain a satisfactory level of attenuation in vivo. Since such a balance could be achieved most directly by genetic engineering, we are analyzing mutations that accumulated during serial passage of the HM-175 strain of hepatitis A virus in MRC-5 cell cultures in order to determine the relative importance of the mutations for growth in MRC-5 cells and for attenuation in susceptible primates. Chimeric viral genomes of the HM-175 strain were constructed from cDNA clones derived from a virulent virus and from two attenuated viruses adapted to growth in African green monkey kidney (AGMK) and MRC-5 cells, respectively. Viruses encoded by these chimeric genomes were recovered by in vitro or in vivo transfection and assessed for their ability to grow in cultured MRC-5 cells or to cause hepatitis in primates (tamarins). The only MRC-5-specific mutations that substantially increased the efficiency of growth in MRC-5 cells were a group of four mutations in the 5' noncoding (NC) region. These 5' NC mutations and a separate group of 5' NC mutations that accumulated during earlier passages of the HM-175 virus in primary AGMK cells appeared, independently and additively, to result in decreased biochemical evidence of hepatitis in tamarins. However, neither group of 5' NC mutations had a demonstrable effect on the extent of virus excretion or liver pathology in these animals.

Independent deposition of heterogeneous nuclear ribonucleoproteins and small nuclear ribonucleoprotein particles at sites of transcription.

The major nuclear ribonucleoproteins (RNPs) involved in pre-mRNA processing are classified in broad terms either as small nuclear RNPs (snRNPs), which are major participants in the splicing reaction, or heterogeneous nuclear RNPs (hnRNPs), which traditionally have been thought to function in general pre-mRNA packaging. We obtained antibodies that recognize these two classes of RNP in Drosophila melanogaster. Using a sequential immunostaining technique to compare directly the distribution of these RNPs on Drosophila polytene chromosomes, we found that the two patterns were very similar qualitatively but not quantitatively, arguing for the independent deposition of the two RNP types and supporting a role for hnRNP proteins, but not snRNPs, in general transcript packaging.