Biomedical subjects

W Filipowicz

Publications and source records attributed to W Filipowicz.

At least 37 records · Page 2Linked to original sources

PubMed1998

Characterization of the Escherichia coli RNA 3'-terminal phosphate cyclase and its sigma54-regulated operon.

The RNA 3'-terminal phosphate cyclase catalyzes the ATP-dependent conversion of the 3'-phosphate to the 2',3'-cyclic phosphodiester at the end of various RNA substrates. Recent cloning of a cDNA encoding the human cyclase indicated that genes encoding cyclase-like proteins are conserved among Eucarya, Bacteria, and Archaea. The protein encoded by the Escherichia coli gene was overexpressed and shown to have the RNA 3'-phosphate cyclase activity (Genschik, P., Billy, E., Swianiewicz, M., and Filipowicz, W. (1997) EMBO J. 16, 2955-2967). Analysis of the requirements and substrate specificity of the E. coli protein, presented in this work, demonstrates that properties of the bacterial and human enzymes are similar. ATP is the best cofactor (Km = 20 microM), whereas GTP (Km = 100 microM) and other nucleoside triphosphates (NTPs) act less efficiently. The enzyme undergoes nucleotidylation in the presence of [alpha-32P]ATP and, to a lesser extent, also in the presence of other NTPs. Comparison of 3'-phosphorylated oligoribonucleotides and oligodeoxyribonucleotides of identical sequence demonstrated that the latter are at least 300-fold poorer substrates for the enzyme. The E. coli cyclase gene, named rtcA, forms part of an uncharacterized operon containing two additional open reading frames (ORFs). The ORF positioned immediately upstream, named rtcB, encodes a protein that is also highly conserved between Eucarya, Bacteria, and Archaea. Another ORF, called rtcR, is positioned upstream of the rtcA/rtcB unit and is transcribed in the opposite direction. It encodes a protein having features of sigma54-dependent regulators. By overexpressing the N-terminally truncated form of RtcR, we demonstrate that this regulator indeed controls expression of rtcA and rtcB in a sigma54-dependent manner. Also consistent with the involvement of sigma54, the region upstream of the transcription start site of the rtcA/rtcB mRNA contains the -12 and -24 elements, TTGCA and TGGCA, respectively, characteristic of sigma54-dependent promoters. The cyclase gene is nonessential as demonstrated by knockout experiments. Possible functions of the cyclase in RNA metabolism are discussed.

Amino Acid Sequence↗

PubMed1998

The host gene for intronic U17 small nucleolar RNAs in mammals has no protein-coding potential and is a member of the 5'-terminal oligopyrimidine gene family.

Intron-encoded U17a and U17b RNAs are members of the H/ACA-box class of small nucleolar RNAs (snoRNAs) participating in rRNA processing and modification. We have investigated the organization and expression of the U17 locus in human cells and found that intronic U17a and U17b sequences are transcribed as part of the three-exon transcription unit, named U17HG, positioned approximately 9 kb upstream of the RCC1 locus. Comparison of the human and mouse U17HG genes has revealed that snoRNA-encoding intron sequences but not exon sequences are conserved between the two species and that neither human nor mouse spliced U17HG poly(A)+ RNAs have the potential to code for proteins. Analyses of polysome profiles and effects of translation inhibitors on the abundance of U17HG RNA in HeLa cells indicated that despite its cytoplasmic localization, little if any U17HG RNA is associated with polysomes. This distinguishes U17HG RNA from another non-protein-coding snoRNA host gene product, UHG RNA, described previously (K. T. Tycowski, M. D. Shu, and J. A. Steitz, Nature 379:464-466, 1996). Determination of the 5' terminus of the U17HG RNA revealed that transcription of the U17HG gene starts with a C residue followed by a polypyrimidine tract, making this gene a member of the 5'-terminal oligopyrimidine (5'TOP) family, which includes genes encoding ribosomal proteins and some translation factors. Interestingly, other known snoRNA host genes, including the UHG gene (Tycowski et al., op. cit.), have features of the 5'TOP genes. Similar characteristics of the transcription start site regions in snoRNA host and ribosomal protein genes raise the possibility that expression of components of ribosome biogenesis and translational machineries is coregulated.

3T3 Cells↗

PubMed1998

Cyclases of the 3'-terminal phosphate in RNA: a new family of RNA processing enzymes conserved in eucarya, bacteria and archaea.

The 2',3'-cyclic phosphate termini are produced, as either intermediates or final products, during RNA cleavage by many different endoribonucleases. Likewise, ribozymes such as hammerheads, hairpins, or the hepatitis delta ribozyme, generate 2',3'-cyclic phosphate ends. Discovery of the RNA 3'-terminal phosphate cyclase has indicated that cyclic phosphate termini in RNA can also be produced by an entirely different mechanism. The RNA 3'-phosphate cyclase converts the 3'-terminal phosphate in RNA into the 2',3'-cyclic phosphodiester in the ATP-dependent reaction which involves formation of the covalent cyclase-AMP and the RNA-N3' pp5' A intermediates. The findings that several eukaryotic and prokaryotic RNA ligases require the 2',3'-cyclic phosphate for the ligation of RNA molecules raised a possibility that the RNA 3'-phosphate cyclase may have an anabolic function in RNA metabolism by generating terminal cyclic groups required for ligation. Recent cloning of a cDNA encoding the human cyclase indicated that genes encoding cyclase-like proteins are conserved among Eucarya, Bacteria, and Archaea. The protein encoded by the Escherichia coli gene was overexpressed and shown to have the RNA 3'-phosphate cyclase activity. This article reviews properties of the human and bacterial cyclases, their mechanism of action and substrate specificity. Possible biological functions of the enzymes are also discussed.

Archaea↗

PubMed1997

Cloning and characterization of the Arabidopsis cyclic phosphodiesterase which hydrolyzes ADP-ribose 1'',2''-cyclic phosphate and nucleoside 2',3'-cyclic phosphates.

In eukaryotic cells, pre-tRNAs spliced by a pathway that produces a 3',5'-phosphodiester, 2'-phosphomonoester linkage contain a 2'-phosphate group adjacent to the tRNA anticodon. This 2'-phosphate is transferred to NAD to give adenosine diphosphate (ADP)-ribose 1", 2"-cyclic phosphate (Appr>p), which is subsequently metabolized to ADP-ribose 1"-phosphate (Appr-1"p). The latter reaction is catalyzed by a cyclic phosphodiesterase (CPDase), previously identified in yeast and wheat. In the work presented here, we describe cloning of the Arabidopsis cDNA encoding the 20-kDa CPDase that hydrolyzes Appr>p to Appr-1"p. Properties of the bacterially overexpressed and purified Arabidopsis enzyme are similar to those of wheat CPDase. In addition to their transformation of Appr>p, both enzymes hydrolyze nucleoside 2',3'-cyclic phosphates to nucleoside 2'-phosphates. For the Arabidopsis CPDase, the apparent Km values for Appr>p, A>p, C>p, G>p, and U>p are 1.35, 1.34, 2.38, 16.86, and 17.67 mM, respectively. Southern analysis indicated that CPDase in Arabidopsis is encoded by a single copy gene that is expressed, at different levels, in all Arabidopsis organs that were analyzed. Indirect immunofluorescence, performed with transfected protoplasts, showed that CPDase is localized in the cytoplasm. Based on substrate specificity and products generated, the plant enzyme differs from other known cyclic phosphodiesterases. The Arabidopsis CPDase does not have recognizable structural similarity or motifs in common with proteins deposited in public data bases.

Adenosine Diphosphate Ribose↗

PubMed1997

The human RNA 3'-terminal phosphate cyclase is a member of a new family of proteins conserved in Eucarya, Bacteria and Archaea.

RNA 3'-terminal phosphate cyclase catalyses the ATP-dependent conversion of the 3'-phosphate to a 2',3'-cyclic phosphodiester at the end of RNA. The physiological function of the cyclase is not known, but the enzyme could be involved in the maintenance of cyclic ends in tRNA splicing intermediates or in the cyclization of the 3' end of U6 snRNA. In this work, we describe cloning of the human cyclase cDNA. The purified bacterially overexpressed protein underwent adenylylation in the presence of [alpha-32P]ATP and catalysed cyclization of the 3'-terminal phosphate in different RNA substrates, consistent with previous findings. Comparison of oligoribonucleotides and oligodeoxyribonucleotides of identical sequence demonstrated that the latter are approximately 500-fold poorer substrates for the enzyme. In Northern analysis, the cyclase was expressed in all analysed mammalian tissues and cell lines. Indirect immunofluorescence, performed with different transfected mammalian cell lines, showed that this protein is nuclear, with a diffuse nucleoplasmic localization. The sequence of the human cyclase has no apparent motifs in common with any proteins of known function. However, inspection of the databases identified proteins showing strong similarity to the enzyme, originating from as evolutionarily distant organisms as yeast, plants, the bacterium Escherichia coli and the archaeon Methanococcus jannaschii. The overexpressed E. coli protein has cyclase activity similar to that of the human enzyme. The conservation of the RNA 3'-terminal phosphate cyclase among Eucarya, Bacteria and Archaea argues that the enzyme performs an important function in RNA metabolism.

Amino Acid Sequence↗

PubMed1996

Characterization of intronic uridine-rich sequence elements acting as possible targets for nuclear proteins during pre-mRNA splicing in Nicotiana plumbaginifolia.

Introns of nuclear pre-mRNAs in dicotyledonous plants, unlike introns in vertebrates or yeast, are distinctly rich in A+U nucleotides and this feature is essential for their processing. In order to define more precisely sequence elements important for intron recognition in plants, we investigated the effects of short insertions, either U-rich or A-rich, on splicing of synthetic introns in transfected protoplast of Nicotiana plumbaginifolia. It was found that insertions of U-rich (sequence UUUUUAU) but not A-rich (AUAAAAA) segments can activate splicing of a GC-rich synthetic infron, and that U-rich segments, or multimers thereof, can function irrespective of the site of insertion within the intron. Insertions of multiple U-rich segments, either at the same or different locations, generally had an additive, stimulatory effect on splicing. Mutational analysis showed that replacement of one or two U residues in the UUUUUAU sequence with A or C residues had only a small effect on splicing, but replacement with G residues was strongly inhibitory. Proteins that interact with fragments of natural and synthetic pre-mRNAs in vitro were identified in nuclear extracts of N.plumbaginifolia by UV cross- linking. The profile of cross-linked plant proteins was considerably less complex than that obtained with a HeLa cell nuclear extract. Two major cross-linkable plant proteins had apparent molecular mass of 50 and 54 kDa and showed affinity for oligouridilates present in synGC introns or for poly(U).

Base Sequence↗

PubMed1996

Splicing of precursors to mRNA in higher plants: mechanism, regulation and sub-nuclear organisation of the spliceosomal machinery.

The removal of introns from pre-mRNA transcripts and the concomitant ligation of exons is known as pre-mRNA splicing. It is a fundamental aspect of constitutive eukaryotic gene expression and an important level at which gene expression is regulated. The process is governed by multiple cis-acting elements of limited sequence content and particular spatial constraints, and is executed by a dynamic ribonucleoprotein complex termed the spliceosome. The mechanism and regulation of pre-mRNA splicing, and the sub-nuclear organisation of the spliceosomal machinery in higher plants is reviewed here. Heterologous introns are often not processed in higher plants indicating that, although highly conserved, the process of pre-mRNA splicing in plants exhibits significant differences that distinguish it from splicing in yeast and mammals. A fundamental distinguishing feature is the presence of and requirement for AU or U-rich intron sequence in higher-plant pre-mRNA splicing. In this review we document the properties of higher-plant introns and trans-acting spliceosomal components and discuss the means by which these elements combine to determine the accuracy and efficiency of pre-mRNA processing. We also detail examples of how introns can effect regulated gene expression by affecting the nature and abundance of mRNA in plants and list the effects of environmental stresses on splicing. Spliceosomal components exhibit a distinct pattern of organisation in higher-plant nuclei. Effective probes that reveal this pattern have only recently become available, but the domains in which spliceosomal components concentrate were identified in plant nuclei as enigmatic structures some sixty years ago. The organisation of spliceosomal components in plant nuclei is reviewed and these recent observations are unified with previous cytochemical and ultrastructural studies of plant ribonuleoprotein domains.

Cell Nucleus↗

PubMed1996

Mapping of branchpoint nucleotides in mutant pre-mRNAs expressed in plant cells.

Pre-mRNA encoding rubisco activase in the Arabidopsis thaliana mutant rca contains a GU to AU change at the 5' splice site of intron 3 and this mutation results in accumulation of splicing intermediates bearing an incompletely processed intron. It has been demonstrated that one of the intermediates contains intron 3 in the form of a lariat and the branchpoint nucleotide has been mapped to the A residue at position -32 forming part of the sequence UUGAU. Analysis of a similar GU to AU 5' splice site mutation, present in a synthetic pre-mRNA context expressed in transfected protoplasts of Nicotiana plumbaginifolia, also suggests formation of lariats with branching occurring at A-31. A small fraction (approximately 10%) of this mutant pre-mRNA also underwent the second step of splicing. In addition to the consensus AG, an AU dinucleotide was used as splicing acceptor.

Arabidopsis↗

PubMed1996

Characterization of the intron-encoded U19 RNA, a new mammalian small nucleolar RNA that is not associated with fibrillarin.

We have characterized a new member (U19) of a group of mammalian small nuclear RNAs that are not precipitable with antibodies against fibrillarin, a conserved nucleolar protein associated with most of the small nucleolar RNAs characterized to date. Human U19 RNA is 200 nucleotides long and possesses 5'-monophosphate and 3'-hydroxyl termini. It lacks functional boxes C and D, sequence motifs required for fibrillarin binding in many other snoRNAs. Human and mouse RNA are 86% homologous and can be folded into similar secondary structures, a finding supported by the results of nuclease probing of the RNA. In the human genome, U19 RNA is encoded in the intron of an as yet not fully characterized gene and could be faithfully processed from a longer precursor RNA in HeLa cell extracts. During fractionation of HeLa cell nucleolar extracts on glycerol gradients, U19 RNA was associated with higher-order structures of approximately 65S, cosedimenting with complexes containing 7-2/MRP RNA, a conserved nucleolar RNA shown to be involved in 5.8S rRNA processing in yeast cells.

Animals↗

PubMed1995

An upstream U-snRNA gene-like promoter is required for transcription of the Arabidopsis thaliana 7SL RNA gene.

The genes transcribed by RNA polymerase (pol) III can be placed into four distinct groups based on the nature and position of their promoter elements. In the higher eukaryotes equivalent genes usually belong to the same sub-type of pol III promoters and there are few examples of genes which have changed promoter type during evolution. In this work we demonstrate that the promoter of the Arabidopsis thaliana 7SL RNA gene is located upstream of the coding region and is identical to the promoters of pol III-specific plant U-small nuclear RNA (U-snRNA) genes. Sequence analysis of two different 7SL genes from A. thaliana revealed that both genes contain two sequence elements in their 5' flanking regions identical in sequence and position to the highly conserved USE and TATA elements of the pol III-transcribed plant U-snRNA genes. Mutational analysis of these elements in the At7SL-2 gene indicates that the USE and TATA elements are both necessary and account for > or = 90% of the transcriptional activity of this gene in transfected plant protoplasts. Within the coding region of both genes there is a sequence element which is a 10/11 nt match to the consensus B-box element of tRNA genes, however, this element is not important for gene activity. These findings distinguish the plant genes from the human 7SL gene, which has both internal and upstream promoter elements and its upstream elements are different from those found in the human U-snRNA genes.

Arabidopsis↗

PubMed1995

Exonucleolytic processing of small nucleolar RNAs from pre-mRNA introns.

Many small nucleolar RNAs (snoRNAs) in vertebrates are encoded within introns of protein genes. We have reported previously that two isoforms of human U17 snoRNA are encoded in introns of the cell-cycle regulatory gene, RCC1. We have now investigated the mechanism of processing of U17 RNAs and of another intron-encoded snoRNA, U19. Experiments in which the processing of intronic RNA substrates was tested in HeLa cell extracts suggest that exonucleases rather than endonucleases are involved in the excision of U17 and U19 RNAs: (1) Cutoff products that would be expected from endonucleolytic cleavages were not detected; (2) capping or circularization of substrates inhibited formation of snoRNAs; and (3) U17 RNA was faithfully processed from a substrate carrying unrelated flanking sequences. To study in vivo processing the coding regions of snoRNAs were inserted into intron 2 of the human beta-globin gene. Expression of resulting pre-mRNAs in simian COS cells resulted in formation of correctly processed snoRNAs and of the spliced globin mRNA, demonstrating that snoRNAs can be excised from a nonhost intron and that their sequences contain all the signals essential for accurate processing. When the U17 sequence was placed in a beta-globin exon, no formation of U17 RNA took place, and when two U17 RNA-coding regions were placed in a single intron, doublet U17 RNA molecules accumulated. The results support a model according to which 5'-->3' and 3'-->5' exonucleases are involved in maturation of U17 and U19 RNAs and that excised and debranched introns are the substrates of the processing reaction.

Base Sequence↗

PubMed1995

Effects of secondary structure on pre-mRNA splicing: hairpins sequestering the 5' but not the 3' splice site inhibit intron processing in Nicotiana plumbaginifolia.

We have performed a systematic study of the effect of artificial hairpins on pre-mRNA splicing in protoplasts of a dicot plant, Nicotiana plumbaginifolia. Hairpins with a potential to form 18 or 24 bp stems strongly inhibit splicing when they sequester the 5' splice site or are placed in the middle of short introns. However, similar 24 bp hairpins sequestering the 3' splice site do not prevent this site from being used as an acceptor. Utilization of the stem-located 3' site requires that the base of the stem is separated from the upstream 5' splice site by a minimum of approximately 45 nucleotides and that another 'helper' 3' splice site is present downstream of the stem. The results indicate that the spliceosome or factors associated with it may have a potential to unfold secondary structure present in the downstream portion of the intron, prior to or at the step of the 3' splice site selection. The finding that the helper 3' site is required for utilization of the stem-located acceptor confirms and extends previous observations, obtained with HeLa cell in vitro splicing systems, indicating that the 3' splice site may be recognized at least twice during spliceosome assembly.

Base Sequence↗

PubMed1995

Extreme heterogeneity of polyadenylation sites in mRNAs encoding chloroplast RNA-binding proteins in Nicotiana plumbaginifolia.

We have previously characterized nuclear cDNA clones encoding two RNA binding proteins, CP-RBP30 and CP-RBP-31, which are targeted to chloroplasts in Nicotiana plumbaginifolia. In this report we describe the analysis of the 3'-untranslated regions (3'-UTRs) in 22 CP-RBP30 and 8 CP-RBP31 clones which reveals that mRNAs encoding both proteins have a very complex polyadenylation pattern. Fourteen distinct poly(A) sites were identified among CP-RBP30 clones and four sites among the CP-RBP31 clones. The authenticity of the sites was confirmed by RNase A/T1 mapping of N. plumbaginifolia RNA. CP-RBP30 provides an extreme example of the heterogeneity known to be a feature of mRNA polyadenylation in higher plants. Using PCR we have demonstrated that CP-RBP genes in N. plumbaginifolia and N. sylvestris, in addition to the previously described introns interrupting the coding region, contain an intron located in the 3' non-coding part of the gene. In the case of the CP-RBP31, we have identified one polyadenylation event occurring in this intron.

Base Sequence↗

PubMed1994

tRNA splicing in yeast and wheat germ. A cyclic phosphodiesterase implicated in the metabolism of ADP-ribose 1",2"-cyclic phosphate.

Adenosine diphosphate (ADP)-ribose 1",2"-cyclic phosphate (Appr > p) is produced as a result of transfer RNA (tRNA) splicing in the yeast Saccharomyces cerevisiae and probably in other eukaryotes. Endonucleolytic cleavage and ligation result in a mature length tRNA with a 2'-phosphate at the splice junction. This 2'-phosphate is transferred to NAD to produce Appr > p. Metabolism of Appr > p requires hydrolysis of the 1",2"-cyclic phosphate linkage. We show here that yeast has a unique cyclic phosphodiesterase that can hydrolyze Appr > p, ribose 1,2-cyclic phosphate, and ribose 1,3-cyclic phosphate to the corresponding ribose 1-phosphate derivatives. The cyclic phosphodiesterase is highly specific for Appr > p; there is 20-fold less activity on ribose 1,3-cyclic phosphate and no detectable activity on nucleoside 2',3'-cyclic phosphates. A similar cyclic phosphodiesterase is present in wheat germ. The wheat germ cyclic phosphodiesterase activity co-chromatographs with a 2',3'-cyclic nucleotide 3'-phosphodiesterase that was previously identified and purified. The purified wheat germ enzyme has a distinct preference for Appr > p and ribose cyclic phosphate compared to guanosine 2',3'-cyclic phosphate and shares other biochemical characteristics with the yeast enzyme.

Adenosine Diphosphate Ribose↗

PubMed1994

Characterisation and expression of a maize U3 snRNA gene.

We have used a probe encoding a U3snRNA gene of Arabidopsis to isolate maize U3snRNA genomic sequences. Of two clones sequenced, one encodes a single U3 gene which has been shown to be expressed in transfected maize protoplasts. The second clone encodes a U3 related sequence which appears to be an RNA-mediated pseudogene.

Arabidopsis↗

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↗

PubMed1993

Activity of U-snRNA genes with modified placement of promoter elements in transfected protoplasts and stably transformed tobacco.

In higher plants the promoter elements of pol II- and pol III-transcribed U-snRNA genes are identical, comprising a -30 TATA box and an upstream sequence element, USE. The USE and TATA are centred approximately four and three helical DNA turns apart in pol II and pol III genes, respectively, and it is this difference in the element spacing that determines the RNA polymerase specificity of the gene. In this study we have analyzed the effect of spacing mutations on activity of Arabidopsis U2 and U6 genes in transfected protoplasts of Nicotiana plumbaginifolia and in stably transformed tobacco. In the pol III-transcribed U6 gene the insertions and deletions of either odd or even numbers of half helical turns completely inactivate transcription in transfected protoplasts, consistent with the high conservation of the element spacing found in all plant U-snRNA genes. Surprisingly, while insertions of 50 base pairs (bp) or more into the spacer of the pol II-specific U2 gene inactivate transcription, a deletion of 5 bp or insertions of as much as 20 bp decrease transcription by only 40 to 70%. This relaxed requirement for the conserved element spacing is only seen in transfected protoplasts since the same mutant U2 genes are not transcribed in stably transformed tobacco when transcription takes place from the chromosome. The results provide some clues about possible factor interactions at the promoters of plant U-snRNA genes and also offer an example of major differences in transcription between transiently and stably transformed cells.

Arabidopsis↗

PubMed1993

Small nucleolar RNAs encoded by introns of the human cell cycle regulatory gene RCC1.

Eukaryotic cells contain a large number of U small nuclear RNAs (U-snRNAs) involved in various RNA processing reactions in the nucleoplasm and nucleous. Most of the U-snRNAs have 5'-terminal caps added to the end of the primary transcript. Here we describe two variants of a snRNA, called U17, identified in human HeLa cells. U17 RNA may be involved in ribosome biogenesis since it is found in the nucleolus and sediments with 40S structures possibly representing nascent ribosomal subunits. U17 RNAs contain no cap but have a monophosphate at the 5'-terminus indicating that they are processed from longer precursors. The U17 RNAs are encoded within introns 1 and 2 of the single copy gene RCC1 which codes for an important cell cycle regulatory protein. In HeLa cell S-100 extract, U17 RNA is faithfully excised from a longer RNA transcript derived from the intron yielding 5'-monophosphorylated RNA. These data suggest that U17 RNAs are not independently transcribed but are processed out of the RCC1 pre-mRNA or out of the spliced introns.

Base Sequence↗