Are U4 small nuclear ribonucleoproteins involved in polyadenylation?

The cDNA sequences of the sea urchin U7 small nuclear RNA suggest specific contacts between histone mRNA precursor and U7 RNA during RNA processing

3' Processing of sea urchin H3 histone pre-mRNA depends on a small nuclear RNP which contains an RNA of nominally 60 nucleotide length, referred to below as U7 RNA. The U7 RNA can be enriched by precipitation of sea urchin U-snRNPs with human systematic lupus erythematosus antiserum of the Sm serotype. We have prepared cDNA clones of U7 RNA and determined by hybridization techniques that this RNA is present in sea urchin eggs at 30-fold lower molar concentration than U1 RNA. The RNA sequences derived from an analysis of eight U7 cDNA clones show neither homologies nor complementarities to any other know U-RNAs. The 3' portion of the presumptive RNA sequence can be folded into a stem-loop structure. The 5'-terminal sequences would be largely unstructured as free RNA. Their most striking feature is their base complementarity to the 3' conserved sequences of histone pre-mRNAs. Six out of nine bases of the conserved CAAGAAAGA sequence of the histone mRNA precursor and 13 out of 16 nucleotides from the conserved palindrome can be base paired with presumptive U7 RNA sequence, suggesting a unique hybrid structure for a processing intermediate formed from histone precursor and U7 RNA.

A sequence downstream of AAUAAA is required for rabbit beta-globin mRNA 3'-end formation

The sequence AAUAAA, found 11-30 base pairs (bp) upstream of the poly(A) site of most non-histone eukaryotic messenger RNAs (mRNAs) forms an essential part of the recognition site for 3'-end processing of the primary transcript. However, the sequence AATAAA is found in transcribed regions of genes and is differentially utilized in genes containing multiple copies of the sequence within the 3'-noncoding region, suggesting that the hexanucleotide alone does not comprise a complete recognition site. Therefore, it seems likely that additional sequences are required to form a complete recognition site for 3'-end formation. We have investigated the sequence requirements for mRNA 3'-end formation using the rabbit beta-globin gene as a model system. Here we demonstrate that an additional sequence 3' to AAUAAA is required for the correct 3'-end formation of rabbit beta-globin mRNA.

Processing and nucleo-cytoplasmic transport of histone gene transcripts

Precursors of Xenopus and sea urchin histone mRNAs were synthesized in vitro with the SP6 transcription system, and their maturation and nucleo-cytoplasmic transport was studied by frog oocyte injection. 3' processing is most rapid for homologous histone messenger sequences and does not require either genuine 5' or specific 3' ends of the precursor, but capping of the 5' terminus strongly influences the efficiency of 3' processing. No generation of 5' histone mRNA ends can be detected when precursors containing 5' spacer sequence extensions are injected into the oocyte nucleus. This finding may have some implications for the question whether histone gene transcription could be polycistronic. Using a novel oocyte technique, we have separated nuclei from cytoplasm and have studied the time course of exit of the processed RNA from the oocyte nucleus into the cytoplasm. The results suggest that RNA maturation and nucleo-cytoplasmic transport are not temporally coupled processes.

Comparison of the whey acidic protein genes of the rat and mouse

Whey acidic protein (WAP), a hormonally-regulated 14,000 dalton cysteine-rich protein, is the principal whey protein found in rodent milk. Genomic clones encompassing both the 2.8 Kb rat and 3.3 Kb mouse WAP genes have been characterized. The genes consist of four exons and three introns. The middle two exons encode the two cysteine-rich regions which probably form separate protein domains. Homology in the 5' flanking DNA of the mouse and rat extends at least 325 bp upstream of the putative CAP site, including a precisely conserved stretch of 50 bp around the unusual TATA and CAAT sites. The homology previously observed between the 3' noncoding sequences of the rat and mouse mRNAs extends at least 20 bp into the 3' flanking region. Several potential glucocorticoid receptor binding sites have been found in the 5' flanking region of the WAP gene. The conservation of the 5' flanking region of the WAP genes may be related to regulation of expression of WAP by peptide and/or steroid hormones.

Characterization of the human factor VIII gene

The complete 186,000 base-pair (bp) human factor VIII gene has been isolated and consists of 26 exons ranging in size from 69 to 3,106 bp and introns as large as 32.4 kilobases (kb). Nine kb of mRNA and protein-coding DNA has been sequenced and the mRNA termini have been mapped. The relationship between internal duplications in factor VIII and evolution of the gene is discussed.

Isolation of a cDNA clone encoding rat insulin-like growth factor-II precursor

Insulin-like growth factor-I (IGF-I) and IGF-II are mitogenic polypeptides of relative molecular mass (Mr) approximately 7,500 isolated from human plasma each containing four peptide domains in a single chain and identical at more than 60% of their amino acid loci. The B- and A-domains of the IGFs are approximately 40% identical to the B- and A-chains of human insulin. IGF-I and IGF-II have similar in vitro biological activities and receptor reactivity, but are immunologically distinct. IGF-I appears to mediate the effects of growth hormone on cartilage to promote skeletal growth whereas IGF-II may have a special role in fetal development and in the central nervous system. To investigate the in vivo role of IGF-II, we have studied IGF-II biosynthesis in the BRL-3A rat liver cell line. BRL-3A cells synthesize and secrete a 7,484 Mr protein 93% identical to human IGF-II and representing rat IGF-II (rIGF-II). Rat IGF-II is synthesized as a approximately 22,000 Mr prepro-rIGF-II (ref. 12) from 12 S poly(A)+mRNA. In addition, approximately 20,000 Mr pro-rIGF-II has been identified in lysates of biosynthetically labelled intact BRL-3A cells. We report here the isolation of an almost complete cDNA clone for rIGF-II. Our results indicate that pro-rIGF-II is synthesized as a 156 amino acid peptide precursor (17,619 Mr) containing mature rIGF-II 1-67 at its amino-terminus and an 89-residue carboxy-terminal peptide extension.

Identification of a small RNA containing the trypanosome spliced leader: a donor of shared 5' sequences of trypanosomatid mRNAs?

The 35 nucleotide spliced leader (SL) sequence is found on the 5' end of numerous trypanosome mRNAs, yet the tandemly organized reiteration units encoding this leader are not detectably linked to any of these structural genes. Here we report the presence of a class of discrete small SL RNA molecules that are derived from the genomic SL reiteration units of Trypanosoma brucei, Trypanosoma cruzi, and Leptomonas collosoma. These small SL RNAs are 135, 105, and 95 nucleotides, respectively, and contain a 5'-terminal SL or SL-like sequence. S1 nuclease analyses demonstrate that these small SL RNAs are transcribed from continuous sequence within the respective SL reiteration units. With the exception of the SL sequence and a concensus donor splice site immediately following it, these small RNAs are not well conserved. We suggest that the small SL RNAs may function as a donor of the SL sequence in an intermolecular process that places the SL at the 5' terminus of many trypanosomatid mRNAs.

The 3' end of drosophila histone H3 mRNA is produced by a processing activity in vitro

We have examined the process by which the 3' terminus of the Drosophila histone H3 mRNA is produced in vitro. When a template containing a portion of DNA that flanks the normal 3' end of the histone H3 gene and an oligo dC tail on the template strand is transcribed in vitro by Drosophila RNA polymerase II, transcription continues beyond the 3' end of the H3 gene. A processing activity was identified that cleaves the precursor transcript generating an RNA species with the same 3' end as the mature H3 mRNA. The processing activity was partially purified by ion exchange chromatography and sucrose gradient sedimentation. The isolated activity was found to require Mg++ but did not require addition of a nucleoside triphosphate for activity. The activity sedimented with a molecular weight of approximately 140,000 daltons. Transcription of the template and processing of the RNA can be uncoupled in vitro.

A labile phosphodiester bond at the ligation junction in a circular intervening sequence RNA

The excised intervening sequence of the Tetrahymena ribosomal RNA precursor mediates its own covalent cyclization in the absence of any protein. The circular molecule undergoes slow reopening at a single phosphodiester bond, the one that was formed during cyclization. The resulting linear molecule has 5'-phosphate and 3'-hydroxyl termini; these are unusual products for RNA hydrolysis but are typical of the other reactions mediated by this molecule. The reopened circle retains cleavage-ligation activity, as evidenced by its ability to undergo another round of cyclization and reopening. The finding that an RNA molecule can be folded so that a specific phosphate can be strained or activated helps to explain how the activation energy is lowered for RNA self-splicing. The proposed mechanisms may be relevant to several other RNA cleavage reactions that are RNA-mediated.