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PubMed1984

Human genes for U2 small nuclear RNA are tandemly repeated.

We found that the genes for human U2 small nuclear RNA (snRNA) are organized as a nearly perfect tandem array of 10 to 20 copies per haploid genome. Although the coding region for the mature form of U2 RNA was only 188 base pairs (bp) long, the basic repeating unit of the tandem array was 6 kilobase pairs in length. Comparison of DNA sequences immediately upstream from human U1 and U2 genes revealed two regions of strong homology: region I (15 bp long) lay upstream of region II (20 bp long) and was separated from it by about the same distance in U1 genes (25 bp) as in U2 genes (21 bp); however, region I and region II were located 174 bp further upstream from the 5' end of the snRNA coding sequence in U1 genes than in U2 genes. Homologs of region II were also found upstream of the snRNA coding region in a mouse U2 gene and two rat U1 genes. Murphy et al. (Cell 29:265-274, 1982) have found that sequences within region II may function as the equivalent of a TATA box for initiation by RNA polymerase II in vitro at a position 183 bp upstream from the 5' end of the human U1 snRNA coding region. In light of the data reported here, this result suggests that region II does indeed play a role in transcription but that its position relative to the actual initiation site can vary.

Bacteriophage lambda↗

PubMed1991

mRNA-type introns in U6 small nuclear RNA genes: implications for the catalysis in pre-mRNA splicing.

U6 small nuclear RNA is one of the spliceosomal RNAs involved in pre-mRNA splicing. In the fission yeast Schizosaccharomyces pombe, the U6 RNA gene was found to have an intron similar to a nuclear pre-mRNA intron, and it was proposed that the U6 intron might be inserted erroneously during pre-mRNA splicing. Using the polymerase chain reaction, we analyzed the U6 RNA genes of 52 organisms. In addition to the five species of Schizosaccharomyces, we found that the yeast species Rhodotorula hasegawae and Rhodosporidium dacryoidum also have mRNA-type introns in their U6 genes; however, in all the other organisms tested, we found no intron within the region of the U6 gene examined. Four introns and one intron are present in the R. hasegawae and R. dacryoidum U6 genes, respectively; and these introns are located at sites differing from the location of the Schizosaccharomyces U6 intron. Most of the U6 introns locate within the conserved domain, which is strikingly similar in structure to the catalytic center of the negative strand of the satellite RNA of tobacco ring spot virus. The introns of the S. pombe and R. dacryoidum U6 genes are located immediately adjacent to the nucleotides that were shown to be essential for the second step of the splicing reaction. These results support the notion that U6 RNA has a catalytic role in pre-mRNA splicing and that U6 introns originated from insertion of an excised intron during pre-mRNA splicing.

Base Sequence↗

PubMed1981

Human DNA sequences complementary to the small nuclear RNA U2.

Clones containing sequences complementary to the small nuclear RNA U2 were isolated from a human DNA library (1). Three clones, designated U2/4, U2/6 and U2/7 were purified and characterized by restriction enzyme cleavage, hybridization and heteroduplex analysis. Hybridization showed that the three clones each contained one single region which is complementary to U2 RNA. Restriction enzyme cleavage revealed furthermore that the inserted fragments in the three recombinants are different. Heteroduplex analysis identified a 240-380 bp long duplex region in each heteroduplex which includes sequences complementary to U2 RNA. Heteroduplexes between clones U2/4 and U2/7 as well as between U2/4 and U2/6 revealed two additional approximately 200 bp long homologies. The remainder of the inserts were found to lack measurable sequence homology. Two fragments from clone U2/4 were subcloned in the pBR322 vector and the subclones were used to determine the nucleotide sequence of a region in clone U2/4 which is complementary to U2 RNA. A comparison between the established sequence and the sequence for rat U2 RNA (2) reveals several discrepancies.

Base Sequence↗

PubMed1996

Cloning of two proximal sequence element-binding transcription factor subunits (gamma and delta) that are required for transcription of small nuclear RNA genes by RNA polymerases II and III and interact with the TATA-binding protein.

The proximal sequence element (PSE)-binding transcription factor (PTF) specifically recognizes the PSEs of both RNA polymerase II- and RNA polymerase III-transcribed small nuclear RNA (snRNA) genes. We previously have shown that PTF purified from human HeLa cells is a multisubunit complex of four polypeptides designated PTF alpha, -beta, -gamma, and -delta. We now report the isolation and expression of cDNAs encoding PTF gamma and PTF delta, as well as functional studies with cognate antibodies that recognize the native PTF complex in HeLa extracts. Immunoprecipitation studies confirm that the four PTF subunits originally found to copurify during conventional chromatography indeed form a tightly associated complex; they further show that the PTF so defined, including the gamma and delta subunits specifically, is essential for transcription of both class II and class III snRNA genes. Immunoprecipitation assays also show a weak substoichiometric association of the TATA-binding protein (TBP) with PTF, consistent with the previous report of a PTF-related complex (SNAPc) containing substoichiometric levels of TBP and a component (SNAPc43) identical in sequence to the PTF gamma reported here. Glutathione S-transferase pulldown assays further indicate relatively strong direct interactions of both recombinant PTF gamma and PTF delta with TBP, consistent either with the natural association of TBP with PTF in a semistable TBP-TBP-associated factor complex or with possible functional interactions between PSE-bound PTF and TATA-bound TBP during promoter activation. In addition, we show that in extracts depleted of TBP and TBP-associated factors, transcription from the U1 promoter is restored by recombinant TBP but not by TFIID or TFIIIB, indicating that transcription of class II snRNA genes requires a TBP complex different from the one used for mRNA-encoding genes.

Amino Acid Sequence↗

PubMed1990

U1 small nuclear RNA plays a direct role in the formation of a rev-regulated human immunodeficiency virus env mRNA that remains unspliced.

rev-regulated expression of HIV-1 envelope proteins from a simian virus 40 late replacement vector was found to be dependent on the presence of a 5' splice site in the env mRNA in spite of the fact that this mRNA remains unspliced. When the 5' splice site upstream of the env open reading frame was deleted or mutated, expression of envelope protein was lost. RNA analysis of cells transfected with 5' splice-site mutants showed a dramatic reduction in the steady-state levels of env mRNA whether or not rev was present. Envelope expression could be restored in one of the 5' splice-site mutants by cotransfection with a plasmid expressing a suppressor U1 small nuclear RNA containing a compensatory mutation. These experiments show that U1 small nuclear RNA plays a direct and essential role in the formation of an unspliced RNA that is subject to regulation by rev.

Animals↗

PubMed1994

Small nuclear RNA genes transcribed by either RNA polymerase II or RNA polymerase III in monocot plants share three promoter elements and use a strategy to regulate gene expression different from that used by their dicot plant counterparts.

RNA polymerase (Pol) II- and RNA Pol III-transcribed small nuclear RNA (snRNA) genes of dicotyledonous plants contain two essential upstream promoter elements, the USE and TATA. The USE is a highly conserved plant snRNA gene-specific element, and its distance from the -30 TATA box, corresponding to approximately three and four helical DNA turns in Pol III and Pol II genes, respectively, is crucial for determining RNA Pol specificity of transcription. Sequences upstream of the USE play no role in snRNA gene transcription in dicot plants. Here we show that for expression of snRNA genes in maize, a monocotyledonous plant, the USE and TATA elements are essential, but not sufficient, for transcription. Efficient expression of both Pol II- and Pol III-specific snRNA genes in transfected maize protoplasts requires an additional element(s) positioned upstream of the USE. This element, named MSP (for monocot-specific promoter; consensus, RGCCCR), is present in one to three copies in monocot snRNA genes and is interchangeable between Pol II- and Pol III-specific genes. The efficiency of snRNA gene expression in maize protoplast is determined primarily by the strength of the MSP element(s); this contrasts with the situation in protoplasts of a dicot plant, Nicotiana plumbaginifolia, where promoter strength is a function of the quality of the USE element. Interestingly, the organization of monocot Pol III-specific snRNA gene promoters closely resembles those of equivalent vertebrate promoters. The data are discussed in the context of the coevolution of Pol II- and Pol III-specific snRNA gene promoters within many eukaryotic organisms.

Arabidopsis↗

PubMed1989

Transcription of a human U6 small nuclear RNA gene in vivo withstands deletion of intragenic sequences but not of an upstream TATATA box.

Most eukaryotic genes transcribed by RNA polymerase III contain internal control regions. U6 small nuclear RNA genes are transcribed by RNA polymerase III but are unusual in that, at least in vitro, their expression does not require intragenic sequences. Here we show that this is true as well in vivo. A human U6 gene devoid of all but the first 6 and last 10 base-pairs was expressed efficiently after transfection into human 293 cells. We also report data extending the previous identification of 5' flanking sequences important for human U6 gene transcription. Deletion-substitution of a 10 base-pair upstream sequence encompassing the TATATA element (-29 to -24) abolished U6 transcription. A double point mutation in the middle of this element (TATATA-TAGCTA) reduced U6 transcription but not to the extent brought about by TATATA deletion-substitution. These results establish that, in vivo, transcription of human U6 small nuclear RNA is independent of intragenic sequences between nucleotides 6 and 98, and requires the upstream TATATA box.

DNA Mutational Analysis↗

PubMed1992

Interactions of small nuclear RNA's with precursor messenger RNA during in vitro splicing.

Precursor messenger RNA splicing requires multiple factors including U1, U2, U4, U5, and U6 small nuclear RNA's. The crosslinking reagent psoralen was used to analyze the interactions of these RNA's with an adenovirus precursor messenger RNA in HeLa nuclear extract. An endogenous U2-U4-U6 crosslinkable complex dissociated upon incubation with precursor messenger RNA. During splicing, U1, U2, U5, and U6 became crosslinked to precursor messenger RNA and U2, U5, and U6 became crosslinked to excised lariat intron. U2 also formed a doubly crosslinked complex with U6 and precursor messenger RNA. The U1, U5, and U6 crosslinks to the precursor messenger RNA mapped to intron sequences near the 5' splice site, whereas the U2 crosslink mapped to the branch site. The kinetics of crosslink formation and disappearance delineates a temporal pathway for the action of small RNA's in the spliceosome. Potential base pairing interactions between conserved sequences in the small nuclear RNA's and precursor messenger RNA at the sites of crosslinking suggest that the 5' splice site is defined in several steps prior to the first cleavage event.

Adenosine Triphosphate↗

PubMed1983

Sensitivity to UV radiation of small nuclear RNA synthesis in mammalian cells.

It was demonstrated previously that the synthesis of small nuclear RNA (snRNA) species U1 and U2 in human cells is very sensitive to UV radiation. In the present work, the UV sensitivity of U3, U4, and U5 snRNA synthesis is shown to be also high. The synthesis of U1, U2, U3, U4, and U5 snRNAs progressively decreased during the first 2 h after UV irradiation (this was not observed in polyadenylated RNA) and had not returned to normal rates 6 h after UV exposure. In contrast, the restoration of 5.8S rRNA synthesis began immediately after UV irradiation and was essentially complete 6 h later. A small fraction of U1 and U5 (and possibly U2 and U3) snRNA synthesis remained unaffected by high UV doses, when cell radiolabeling began 10 min after UV irradiation. The present data suggest that a factor other than the level of pyrimidine dimers in DNA (possibly, steps in the post-irradiation DNA repair process) plays an important role in the mechanism of UV-induced inhibition of U1-U5 snRNA synthesis.

Carcinoma↗

PubMed1986

Isolation and characterization of two putative full-length Drosophila U4 small nuclear RNA genes.

U4 RNA is one of the abundant small nuclear RNAs implicated in the processing of the 3' -ends of premessenger RNAs (Berget, S. (1984) Nature 309, 179-182). Two potential U4 RNA genes were isolated from a Drosophila genomic DNA library and characterized. These genes, which were from different loci, had transcription and processing signals common to Drosophila U1 and U2 small nuclear RNA genes. One U4 gene locus also contained a downstream 5'-truncated U4 pseudogene. This is the first report in which putative full-length genes for U4 small nuclear RNA were isolated and characterized.

Animals↗

PubMed1984

True genes for human U1 small nuclear RNA. Copy number, polymorphism, and methylation.

The nucleotide sequence of a human U1 small nuclear RNA gene (HU1-1) is presented, along with several hundred nucleotides of its 5' and 3' flanking regions. We demonstrate that the immediate 5' flanking region sequences are a highly specific hydridization probe capable of distinguishing U1 RNA true genes from pseudogenes. The copy number of U1 RNA genes was determined to be constant, about 30/haploid genome equivalent in six different individuals. Nevertheless, several restriction enzyme cleavage site polymorphisms exist in these genes. We also show that C-C-G-G sequences in the vicinity of U1 RNA true genes are not methylated, but they are methylated near pseudogenes. Genomic DNAs of mouse, frog, chicken, and fruit fly contain sequences homologous to the human U1 RNA gene coding region but not to the 5' flanking region. This suggests that sequences important for expression of U1 RNA genes constitute only a minor part of the 5' flanking regions. In the HU1-1 locus, sequences similar to the consensus T-A-T-A-A-A box are located about 45 and 210 base pairs upstream of the point corresponding to the 5' end of the mature RNA. Several additional direct repeats which may be regulatory elements are present in the upstream region. A few short inverted repeats which probably constitute a transcription termination signal are in the region corresponding to the 3' end of the U1 RNA.

Bacteriophage lambda↗

PubMed1984

Localization of human U1 small nuclear RNA genes to band p36.3 of chromosome 1 by in situ hybridization.

U1 small nuclear RNA (U1 snRNA) is encoded by a large family of genes (30-125 copies/haploid genome) which are transcribed by RNA polymerase II. U1 snRNA is thought to function in gene splicing. Since the U1 genes were found to be greater than 20 kb apart by analyzing genomic phage clones, the chromosomal location of U1 genes in the human genome was determined using Southern filter analysis of DNA isolated from human-rodent somatic cell hybrids and by in situ hybridization. Human DNA digested with PvuII and probed with a U1-specific probe, pD2, show several major hybridizing fragments. Of these, two human PvuII fragments of 1.4 kb and 2.4 kb had unique mobilities compared to mouse fragments. In a study of 19 cell hybrids, the human-specific U1 fragments segregated with the chromosome 1 markers peptidase C and adenylate kinase 2. All other chromosomes showed greater than or equal to 19% discordancy . An additional 13 karyotyped cell hybrids, analyzed by Southern filter analysis, confirmed the assignment of this class of U1 genes to chromosome 1. Additional digests with MspI and PstI indicated that most U1 genes are located on chromosome 1. To determine if the U1 RNAs are located predominantly at one site or dispersed over chromosome 1, a tritium-labeled U1 probe was hybridized in situ to metaphase chromosomes. The majority of the grains were at band 1p36 .3, suggesting that most of the U1 genes are located in this region.

Animals↗

PubMed1997

Formation of 2',3'-cyclic phosphates at the 3' end of human U6 small nuclear RNA in vitro. Identification of 2',3'-cyclic phosphates at the 3' ends of human signal recognition particle and mitochondrial RNA processing RNAs.

Approximately 90% of human U6 small nuclear RNA (snRNA) contains uridine cyclic phosphate (U>p) at its 3'-end (Lund, E., and Dahlberg, J. E. (1992) Science 255, 327-330). We studied the formation of U>p at the 3' end of human U6 snRNA using an in vitro system where uridylic acid residues are added from UTP precursor and U>p is formed. Analysis of U6 snRNAs with varying number of uridylic acid residues showed that each of these species contains U>p where the phosphate originated from alpha-phosphate of UTP precursor. The cyclic phosphate formation occurred on U6 snRNA in extracts where essential spliceosomal snRNAs were specifically degraded, thereby indicating that U>p formation is not coupled to pre-mRNA splicing. A subpopulation of human signal recognition particle and mitochondrial RNA processing RNAs isolated from HeLa cells also contained cyclic phosphates at their 3' ends. These data suggest that U>p in U6 snRNA is unlikely to be related to its participation in splicing of pre-mRNAs. It appears that cyclic phosphate is an intermediate product in the metabolism of these small RNAs.

HeLa Cells↗

PubMed1992

Three novel functional variants of human U5 small nuclear RNA.

We have identified and characterized three new variants of U5 small nuclear RNA (snRNA) from HeLa cells, called U5D, U5E, and U5F. Each variant has a 2,2,7-trimethylguanosine cap and is packaged into an Sm-precipitable small nuclear ribonucleoprotein (snRNP) particle. All retain the evolutionarily invariant 9-base loop at the top of stem 1; however, numerous base changes relative to the abundant forms of U5 snRNA are present in other regions of the RNAs, including a loop that is part of the yeast U5 minimal domain required for viability and has been shown to bind a protein in HeLa extracts. U5E and U5F each constitute 7% of the total U5 population in HeLa cells and are slightly longer than the previously characterized human U5 (A, B, and C) species. U5D, which composes 5% of HeLa cell U5 snRNAs, is present in two forms: a full-length species, U5DL, and a shorter species, U5DS, which is truncated by 15 nucleotides at its 3' end and therefore resembles the short form of U5 (snR7S) in Saccharomyces cerevisiae. We have established conditions that allow specific detection of the individual U5 variants by either Northern blotting (RNA blotting) or primer extension; likewise, U5E and U5F can be specifically and completely degraded in splicing extracts by oligonucleotide-directed RNase H cleavage. All variant U5 snRNAs are assembled into functional particles, as indicated by their immunoprecipitability with anti-(U5) RNP antibodies, their incorporation into the U4/U5/U6 tri-snRNP complex, and their presence in affinity-purified spliceosomes. The higher abundance of these U5 variants in 293 cells compared with that in HeLa cells suggests possible roles in alternative splicing.

Base Sequence↗

PubMed1985

U1 small nuclear RNA genes are subject to dosage compensation in mouse cells.

Multiple copies of a gene that encodes human U1 small nuclear RNA were introduced into mouse C127 cells with bovine papilloma virus as the vector. For some recombinant constructions, the human U1 gene copies were maintained extrachromosomally on the viral episome in an unrearranged fashion. The relative abundance of human and mouse U1 small nuclear RNA varied from one cell line to another, but in some lines human U1 RNA accounted for as much as one-third of the total U1. Regardless of the level of human U1 expression, the total amount of U1 RNA (both mouse and human) in each cell line was nearly the same relative to endogenous mouse 5S or U2 RNA. This result was obtained whether measurements were made of total cellular U1 or of only the U1 in small nuclear ribonucleoprotein particles that could be precipitated with antibody directed against the Sm antigen. The data suggest that the multigene families encoding mammalian U1 RNA are subject to some form of dosage compensation.

Animals↗

PubMed1996

Cloning and characterization of the beta subunit of human proximal sequence element-binding transcription factor and its involvement in transcription of small nuclear RNA genes by RNA polymerases II and III.

The proximal sequence element (PSE)-binding transcription factor (PTF), which binds the PSE of both RNA polymerase II- and RNA polymerase III-transcribed mammalian small nuclear RNA (snRNA) genes, is essential for their transcription. We previously reported the purification of human PTF, a complex of four subunits, and the molecular cloning and characterization of PTF gamma and delta subunits. Here we describe the isolation and expression of a cDNA encoding PTF beta, as well as functional studies using anti-PTF beta antibodies. Native PTF beta, in either protein fractions or a PTF-Oct-1-DNA complex, can be recognized by polyclonal antibodies raised against recombinant PTF beta. Immunodepletion studies show that PTF beta is required for transcription of both classes of snRNA genes in vitro. In addition, immunoprecipitation analyses demonstrate that substantial and similar molar amounts of TATA-binding protein (TBP) and TFIIIB90 can weakly associate with PTF at low salt conditions, but this association is dramatically reduced at high salt concentrations. Along with our previous demonstration of both physical interactions between PTF gamma/PTF delta and TBP and the involvement of TFIIIB90 in the transcription of class III snRNA genes, these results are consistent with the notion that a TBP-containing complex related to TFIIIB is required for the transcription of class III snRNA genes, and acts through weak interaction with the four-subunit PTF.

Amino Acid Sequence↗

PubMed1987

Nucleotide sequence of a bean (Phaseolus vulgaris) U1 small nuclear RNA gene: implications for plant pre-mRNA splicing.

We have isolated a U1 small nuclear RNA (snRNA) gene from common bean (Phaseolus vulgaris). The haploid bean genome contains only one or a few copies of the U1 snRNA gene. The bean and human U1 snRNA genes are 65% homologous but share no significant similarity in the 5' or 3' flanking regions. The predicted secondary structure of bean U1 snRNA is identical to that of other U1 snRNAs, and the sequences of the single-stranded regions have been highly conserved. Thus, both the sequence of the single-stranded regions and the secondary structure of U1 snRNA appear to be important for its function. The role of U1 snRNA in pre-mRNA splicing is probably similar in plants and animals.

Base Sequence↗

PubMed1988

U2 small nuclear RNA is remarkably conserved between Schizosaccharomyces pombe and mammals.

We report the molecular cloning and sequencing of the most abundant trimethylguanosine-capped small nuclear RNA from the fission yeast Schizosaccharomyces pombe, a highly conserved homolog of mammalian U2 small nuclear RNA. This RNA is 186 nucleotides in length, just 2 nucleotides shorter than its human counterpart; this is in contrast to Saccharomyces cerevisiae U2, which is 1,175 nucleotides long. Moreover, the secondary structure of Schizosaccharomyces pombe U2 is virtually identical to that of mammalian U2, including the 3' half of the RNA, which shows limited primary sequence identity. Northern (RNA) blot analysis revealed that the size of this RNA is conserved not only in fission yeasts but in many organisms, including other ascomycetes.

Animals↗