SYSTEM FOR REPRODUCING AND MODULATING STABILITY AND TURNOVER OF RNA MOLECULES

Abstract: An <i>in vitro</i> system is provided that recapitulates regulated mRNA stability and turnover of exogenous RNA substrates. The system comprises a cell extract optionally depleted of activity of proteins that bind polyadenylate, and a target RNA sequence. This system is used for the identification of agents capable of modulating RNA turnover, as well as agents capable of modulating RNA turnover in the presence of RNA stability modifying agents.

Description: SYSTEM FOR REPRODUCING AND MODULATING STABILITY AND TURNOVER OF RNA MOLECULES GOVERNMENTAL SUPPORT The research leading to the present invention was supported, at least in part, by grant No. GM56434 from the National Institutes for Health. Accordingly, the Government may have certain rights in the invention. FIELD OF THE INVENTION Broadly, the present invention involves a system and method for monitoring the stability of RNA and identifying agents capable of modulating RNA stability BACKGROUND OF THE INVENTION The relative stability ot a mRNA is an important regulator of gene expression. The half-life of a mRNA plays a role in determining both the steady state level of expression as well as the rate of inducibility of a gene product In general, many short-lived proteins are encoded by short-lived mRNAs Several mRNAs that encode stable proteins, such as α-globin. have also been shown to have extraordinarily long half-lives Suiveillance mechanisms are also used by the cell to identify and shorten the half-lives of mRNAs that contain nonsense codon mutations. Clearly, changes in the half-life of a mRNA can have dramatic consequences on cellular responses and function Little is known about mechanisms of mRNA turnover and stability in mammalian cells, but in vivo data are beginning to allow some generalizations about major pathways of mRNA turnover. The mRNA poly(A) tail can be progressively shortened throughout the lifetime of a mRNA in the cytoplasm. Controlling the rate of this deadenylation process appears to be a target for many factors that regulate mRNA stability. Once the poly(A) tail is shortened to approximately 50- 100 bases, the body of the mRNA is degraded in a rapid fashion with no discernible intermediates. The process of translation also influences mRNA stability. Little is known, however, concerning the enzymes and regulatory components involved in mammalian mRNA turnover. Several cis-acting elements have been shown to play a role in mRNA stability. Terminal (5') cap and 3'-poly(A) structures and associated proteins are likely to protect the transcript from exonucleases. Several destabilizing as well as stabilizing elements located in the body of the mRNA have also been identified. The best characterized instability element is an A-U rich sequence (ARE) found in the 3' untranslated region of many short-lived mRNAs. These AREs primarily consist of AUUUA (SEQ ID NO: 12) repeats or a related nonameric sequence. AREs have been shown to increase the rate of deadenylation and mRNA turnover in a translation-independent fashion. For example, proteins with AU-rich elements include many growth factor and cytokine mRNAs. such as c-fos. c-jun. c-myc TNFα. GMCSF. IL1- 15. and IFN-β. Other stability elements include C-rich stabilizing elements, such as are found in the mRNAs of globin. collagen, lipoxygenase. and tyrosine hydroxylase. Still other mRNAs have as yet uncharacterized or poorly characterized sequence elements, for example, that have been identified by deletion analysis, e.g. VEGF mRNA. Numerous proteins have been described that interact with some specificity with an ARE. but their exact role in the process of mRNA turnover remains to be defined. For example, proteins which bind to the ARE described above include HuR and other ELAv family proteins, such as HuR (also called HuA), Hel-Nl (also called HuB), HuC and HuD: AUF 1 (four isoforms); tristetrapolin; AUH: TIA; TIAR; glyceraldehyde-3 -phosphate: hnRNP C; hnRNP Al : AU-A; and AU-B. Many others have not been extensively characterized. Through the application of genetics, the mechanisms and factors involved in the turnover of mRNA in Saccharomyces cerevisiae are beginning to be identified. One -9- major pathway of mRNA decay involves decapping followed by the action of a 5'-to- 3' exonuclease. Evidence has also been obtained for a role for 3'-to-5' exonucleases in an alternative pathway. Functionally significant interactions between the cap structure and the 3' poly(A) tail of yeast mRNAs have also been described. Several factors involved in the translation-dependent pathway of nonsense-codon-mediated decay have also been identified. Whether these observations are generally applicable to mammalian cells, however, remains to be established. Mechanistic questions in mammalian cells are usually best approached using biochemical systems due to the inherent difficulties with mammalian cells as a genetic system. Thus, efforts have been made to develop in vitro systems to study mRNA stability and turnover. However, the presently available in vitro systems suffer from numerous limitations. For example, many suffer from poor data quality and a general lack of reproducibility that significantly limits their application. Another key problem is that most of these systems do not faithfully reproduce all aspects of mRNA stability. A significant difficulty in the development of these systems is to differentiate between random, non-specific RNA degradation and true, regulated mRNA turnover. The significance of all previous in vitro systems to the true in vivo process of mRNA stability, therefore, is unclear. To date, no in vilro mRNA stability system has been generally accepted in the field as valid and useful. Other problems that have been uncovered in presently available systems are that they usually involve a complicated extract protocol that is not generally reproducible by other laboratories in the field. Also, presently available systems can only be used to assess the stability of endogenous mRNAs. severely limiting their utility. Finally, the data quality obtained using such systems is highly variable, precluding their use in sensitive screening assays. Accordingly, there exists a need for an in vitro RNA stability system is efficient and highly reproducible, and further, one which produces minimal to undetectable amounts of RNA detrradation A further need exists lor an in vitro RNA stability system wherein deadenylation of an RNA transcript in the system should occur before general degradation of the mRNA body is observed. Also needed is an in vitro RNA stability system wherein degradation of the mRNA body occurs in an apparently highly processive fashion without detectable intermediates, and further, the regulation of the rate of overall deadenylation and degradation should be observed in a sequence-specific manner. Such a system should be applicable to exogenous RNAs and allow ease of experimental manipulation. The citation of any reference herein should not be construed as an admission that such reference is available as "Prior Art" to the instant application. SUMMARY OF THE INVENTION In accordance with the present invention, an in vitro system for modulating the stability and turnover of an RNA molecule is provided which models RNA processing in vivo. Thus, the present invention permits high throughput screening of compounds/macromolecules that modulate the stability of eukaryotic RNAs in order to identify and design drugs to affect the expression of selected transcripts, as well as to aid in the characterization of endogenous proteins and other macromolecules involved in mRNA stability. The in vitro system of the present invention is useful as a diagnostic aid for determining the molecular defect in selective disease alleles: development of in vitro mRNA stability systems for other eukaryotic organisms including parasites and fungi which should lead to novel drug discovery: and improving gene delivery systems by using the system to identify factors and RNA sequences that affect RNA stability. Broadly, the present invention extends to an in vitro system capable of recapitulating regulated RNA turnover of an exogenously added preselected target RNA sequence, the system comprising a cell extract and a target RNA sequence. In a non-limiting example of the system described herein the regulated RNA turnovei is ΛU-nch element regulated RNA turnover or C-πch element regulated RNA turnover The cell extract ot the sv stem of the present inv ention is isolated from lysed eukaryotic cells or tissues, the cell exti act may be obtained foi example Irom a cell line, such as HeLa cells or a T cell line, but the invention is not so limited The cell extract may be prepared from cells comprising foreign nucleic acid, such as those that are infected, stably transfected, or transiently transfected The cell extiact mav be partiall purified In one embodiment of the inv ention, the cel l extract mav be depleted of activity of proteins that bind polvadenvlatc The depletion of activitv of pi ote s that bind polyadenylate from the cell extract may be achieved by any of a number oi methods, for example, the addition to the system of polyadenvlate competitor RNA. the sequestration of proteins that bind polyadenylate. the addition of a proteinase that inactivates a protein that bind to polyadenylate. oi addition of an agent that pi events the interaction between polyadenylate and an endogenous maci omoiecule that binds to polyadenylate, to name a few As furthei examples of the methods for sequestration of proteins that bind polyadenylate. it may be achieved by such non- 1 uniting procedures as the treatment of the extract with an material that depletes macromolecules that bind polyadenylate, such as antibodies to proteins that bind polyadenylate. polyadenylate. and the combination The material may be attached to a matrix Other methods to achiev e the depletion of the activity of proteins that bind polyadenylate may be used The target RNA sequence used in the system may be. by way of non-limiting examples. synthetic RNA, naturally occurring RNA. messenger RNA. chemically modified RNA, or RNA-DNA derivatives The target RNA sequence mav have a 5' cap and a 3' polyadenylate sequence The target RNA sequence may be unlabeled target RNA sequence, labeled target RNA sequence, oi a the combination of both The labeled RNA sequence may be labeled with a moiety such as but not limited to a fluorescent moietv . a v isible moiety , a radioactive moiety, a ligand. and a combination of fluoiescent and quenching moieties Other moieties and means for labeling RNA are embraced herein The system of the present invention may additionally include exogenously added nucleotide tπphosphate. ATP is preferred It may also include a reaction enhancer to enhance the interaction between the various components present in the sv stem. for example, polymers such as but not limited to polyvinyl alcohol, poiyvinylpvrrolidone and dextran. polyvinyl alcohol is preferred The present invention is also directed to a method for identifying agents capable of modulating the stabilitv of a target RNA sequence The method is carried out by preparing the system described above which includes the cell extract depleted of activity of proteins that bind polyadenylate and the target RNA sequence, introducing into the aforesaid system an agent to be tested, determining the extent of turnovei of the target RNA sequence by, for example, determining the extent of degradation of the labeled target RNA. and then identifying an agent which is able to modulate the extent of RNA turnover as capable of modulating the stabilitv of the target RNA sequence The method described above may additionally include nucleotide tπphosphate, ATP being preferred The agent to be tested may be, but is not iunited to. an RNA stability modifying molecule The non-limiting selection of the tvpes of tai get RNA sequence and the non- limitmg types of labels useful for the RNA as described hereinabove The method of the present invention is useful for identifying agents which can either increases or decrease the stabilitv of said tai get RNA sequence Such agents may be capable of modulating the activ itv of an RNA binding molecule such as. but not limited to. C-πch element binding proteins and AU rich element binding proteins, examples of the latter including HuR and other ELAv family piotems. such as HuR , Hel-Nl . HuC and HuD, AUF1. tπstetrapohn AUH. TIA. TIAR. glyceraldehvde-3-phosphate. hnRNP C. hnRNP Al AU-A and AU-B This list is provided as illustrative of the types of molecules that may be evaluated in the present invention, but is by no means limiting In a further embodiment of the present invention, a method is provided for identifying an agent that is capable oi modulating the stability of a target RNA sequence in the presence of an exogenously added RNA stability modifier or RNA binding macromolecule Non- limiting examples of such molecules are described abov e The method is carried out by preparing the system described above which includes the cell extiact can be depleted of activity of proteins that bind polvadenylate and the target RNA sequence, introducing into the aforesaid system the exogenously added RNA stability modifier or binding macromolecule and the agent to be tested, determining the extent of turnover of the target RNA sequence bv foi example determining the extent ot degradation of the labeled target RNA. and then identifv mg an agent able to modulating the extent ot the RNA turnover as capable of modulating the stability of the taiget RNA sequence in the presence of the exogenously added RNA stabilitv modifiei The non-limiting selection of the components of this method are as described above The aforementioned method is useful, foi example w hen the RNA stability modifier decreases the stability of said tai get RNA sequence, and the agent to be identified increases the stability of the target RNA sequence that is decreased by the RNA stability modifier In addition, the method is useful when the RNA stability modifier increases the stability ot the target RNA sequence, and the agent to be identified deci eases the stability of the target RNA sequence that is increased by the RNA stability modifier Non-limiting examples of RNA stability modifiers include C-nch element binding proteins, and AU rich element binding proteins, examples of AU nch element binding proteins, including HuR and other ELAv family proteins, such as HuR Hel-N l , HuC and HuD. AUF 1 tnstetrapoiin. AUH. TIA TIAR. glyceιaldehyde-3-phosphate. hnRNP C hnRNP A 1 , Al '-A. and AU-B This list is provided as illustrative of the tvpes of molecules that may be evaluated in the present invention, but is by no means limiting The present invention is further directed to a method foi identifying an agent capable of modulating the deaden vlation of a target RNA sequence comprising preparing the system described above in the absence of nucleotide tnphosphate. such as ATP. introducing an agent into the system, and monitoring the deadenylation of the target RNA sequence Furthermore, the invention is also dn ected towards a method foi identifying an agent capable of modulating the deadenvlation and degradation of a target RNA sequence comprising preparing the system described herein in the presence ot ATP. introducing the agent into the system, and monitoring the deadenvlation and degradation of the target RNA sequence These embodiments mav also be carried out in the presence of an RNA stability modifier or RNA binding macromolecule to determine the ability ot the agent to modulate the effect of the modulator or binding molecule on RNA stability It is a further aspect ot the present invention to provide a method for identifying an agent capable of modulating cell grow th oi cell diffei entiation in a mammal comprising determining the abilitv ot said agent to modulate the stabilitv of a target RNA sequence involved in the modulation of cell growth or differentiation in accordance with the methods described above The agents capable of modulating cell growth or cell differentiation may intervene in such physiological piocesses as cellular transformation and immune dysregulation. but the invention is not so limiting It is yet a further aspect of the present invention to provide a method for identifying, characterizing and isolating an endogenous molecule suspected of participating in the deadenylation or degradation of RNA or regulation thei eof comprising preparing the system described hereinabove. introducing a protein suspected of participating in the regulation of RNA turnov ei into said system, and monitoi ing the stability of the target RNA sequence The endogenous molecule suspected of participating in the deadenylation and/or degradation of RNA or regulation may be protein or RNA In another embodiment ot the invention, a method is pi ovided for identifying an agent capable ot modulating the degradation a target RNA sequence in the absence ot deadenylation comprising providing a cell extract in the presence of a nucleotide tnphosphate. introducing said agent into said cell extract, and monitoring the degradation of said target RNA sequence in said extract A further aspect ot the present invention is directed to a kit for monitoring the stability of a preselected target RNA sequence under conditions capable ot l ecapitulating regulated RNA turnover The kit compnses a cell extract that optionallv may be depleted of activity of proteins that bind polv adenylate. other reagents, and dn ections for use The kit may further comprise nucleotide ti iphosphates. a reaction enhancer or both Accordingly, it is an object of the invention to provide a system for modulating the stability and turnover of an RNA molecule in vitro which permits a skilled artisan to study the turnover generally. 01 deadenylation and degradation specifically, of an RNA transcript, and screen drugs which can modulate the stability and turnover of an RNA transcript The turnover may be in the absence or presence of exogenously added RNA stability modulators, or permit the study of the role of endogenous molecules in RNA turnover It is another embodiment of the invention to provide a kit that a skilled artisan can readily use to modulate the stabilitv and turnover of an RNA molecule in vitro, and investigate the aforementioned agents These and other aspects of the present invention will be better appreciated bv reference to the following drawings and Detailed Description BRIEr DESCRIPTION OF THE DRAWINGS FIG.l A-D The addition of poly(A) to cytoplasmic S 100 extracts activates specific deadenylase and degradation activities Panel A Poly(A) competitor RNA activates nucleolytic activities in the extract A capped, radiolabeled 54 base RNA containing a 60 base poly(A) tail (Gem-A60) was incubated at 30° C with S I 00 extract in the absence (lanes marked S 100) or presence (Lanes maiked S 100 +Poly(A)) of 500 ng of cold poly(A) RNA as described in Materials and Methods of Example I for the times indicated RNA products were analyzed on a 5° o acrylanude gel containing 7M iu ea The position ot a deadenylated, 54 base transcript (Gem-AO) is indicated on the right Panel B The shortening of input transcripts is due to a i -to- 5 exonuclease Gem-A60 R\ A. labeled exclusively at the 5 " cap, was incubated in the in \ ιtro mRNA stabilitv system ioi the times indicated Reaction products were analyzed on a 5% acrylamide gel containing 7M urea The position of a deadenylated. 54 base ti anscnpt (Gem-AO) is indicated on the right Panel C An alternative approach also demonstrates that the shortening of input transcripts is due to a 3 "-to-5' exonuclease ARE-A60 RNA. i adiolabeled at A residues was incubated in the in vitro stability system tor the times indicated Reaction products were hybridized to a DNA oligo and cleaved into 5 and 3 ' fragments using RNase H Fi agments were analyzed on a 5% acrylamide gel containing 7M urea Panel D The 3 ' -to-5 exonuclease activity is a specific deadenylase Gem-A60 RNA or a variant that contains I 8 extra nucleotides after the poIy(A) tract (Gem-A60- 1 5) w ei e incubated in the in I itro stability svstem foi the times indicated RNA products ei e analyzed on a 5% acr lamide gel containing 7M urea The position of a deadenylated. 54 base ti anscnpt (Gem-AO) is indicated on the left 3 1 + 1 1 0% of the input Gem-A60 RNA was deadenylated/degraded in 30 mm FIG. 2 A-E The tate ot transcript degradation in the in vtti o svstem is regulated by AU-πch instability elements in a sequence-specific fashion Panel A. AU-πch elements dramatically increase the rate of turnover in the in vitro svstem Gem-A60 RNA or a polyadenylated transcript that contains the 34 base AU-πch element from the TNF-cc mRNA, were incubated in the in vitro stability svstem for the times indicated RNA products were analyzed on a 5% acrylamide gel containing 7M urea The positions of deadenylated ti anscnpts (Gem-AO and ARE-A0) are indicated The ARE-A60 RNA was deadenv lated/degraded 6 6+0 4 fold fastei than Gem-A60 RNA Panel B. Fhe AU-i ich element t i om c-fos mRNA also functions as an instability element in \ m Gem-A60 RNA oi a transci ipt that contains the 72 base AU-πch element fi om the c-tos mRNA (Fos-A60) w tie incubated in the in Mtro stabilitv system tor the times indicated RNA products were analyzed on a ">% acrvlamide gel containing 7M urea The positions ot deadenvlated transci ψts (Gem ΛO and Fos-AO) are indicated The Fos-A60 RNA was deadenvlated/degraded 3 5±Q 3 fold faster than Gem-A60 RNA Panel C The ability of AU- ch elements to mediate transcript instabilitv in the in vi o system is sequence-specific ARE-A60 RNA 01 a variant that contains a mutation at every fourth position (mt ARE-A60 see Materials and Methods) wei e incubated in the in vitro stability system for the times indicated RNA products were analvzed on a 5% acrylamide gel containing 7M urea The positions of deadenvlated transcripts (ARE-AO and mt ARE-AO) ai e indicated Mutations in the ARE reduced the rate ot deadenvlation/degradation by 3 7+1 4 fold compared to the wild tvpe ARE-A60 transci ipt Panel D. The TNF-α AU-nch element mediates instability in a heterologous context Λ. polvadenylated 250 base RNA derived from the SV late transcription unit (SV-A60), 01 a variant that contains the 34 base AU-nch element from the TNF-α mRNA (SV ARE-A60 ) were incubated in the in vitro stability system toi the times indicated RNA products w ei e analyzed on a ;>% acrylamide gel containing 7M urea 1 he positions ot deadenvlated tianscnpts (SV-AO and SVARE-AO) are indicated SVARE-A60 RNA was deadenvlated/degraded 3 5+0 7 fold faster than SV-A60 RNA Panel E The AU-πch element denved from the GM-CSF mRNA functions in vitro on nearlv a full length RNA substrate A nearlv full length version of the GM-CSF mRNA that contained an AU-nch element (GM-CSF(+ARE), or a version in which the AU-nch element was deleted (GM CSF(-ARE) w ere incubated in the in vitro stability system for the times indicated RNA products were analvzed on a 5% acrylamide gel containing 7M uiea GM-CSF(+ARE) w as deadenvlated/degraded 2 8+0 2 fold faster than the GM-C SF(- ARF) ti anscπpt FIG. 3 A-B: Deadenylation occurs in the absence of ATP and is regulated by AU-rich elements in vitro Panel A. Degradation, but not deadenylation, requires ATP. SV-ARE-A60 RNA was incubated in the in vitro system in the presence ((-t-) ATP lanes) or absence ((-) ATP lanes ) for the times indicated. RNA products were analyzed on a 5% acrylamide gel containing 7M urea. The positions of the deadenylated SVARE-A) transcript is indicated. Panel B. AU-rich elements regulate the rate of deadenylation on RNA substrates which carry a physiologic length poly(A) tail. SV RNA or SV-ARE RNA (a variant that contains an AU-rich element) were polyadenylated with yeast poly(A) polymerase and species that contained tails of approximately 1 50-200 bases were gel purified. These RNAs ( S V( A 1 50-200) and S VARE(A 1 50-200) were incubated in the in vitro stability system for the times indicated. RNA products were analyzed on a 5% acrylamide gel containing 7M urea. The positions of deadenylated transcripts (SV-A0 and SVARE-A0) are indicated. SVARE( A 150-200) RNA was deadenylated 2.2+0.3% fold faster than the SV(A 150-200) transcript. Figure 4 A-B: The HuR protein of the ELAV family specifically binds to the TNF-α AU-rich element in the in vitro system. Panel A. Two proteins specifically interact with the TNF-α AU-rich element. Gem-A60 and ARE-A60 RNAs were radiolabeled at U residues and incubated in the m vitro stability system for 5 min in the presence of EDTA (to block degradation and allow for accurate comparisons). Reaction mixtures were irradiated with UV light, cleaved with RNase A. and protem-RNA complexes were analyzed on a 10% acrylamide gel containing SDS. The approximate sizes of the cross linked proteins indicated on the right were deduced from molecular weight markers. Panel B. The 30 kDa protein is HuR. Radiolabeled ARE-A60 RNA was incubated in the in vitro RNA stability system and cross-linked to associated proteins as described above C ross linked proteins were immunoprecipitated using the indicated antisera prior to analv sis on a 10% acrylamide gel containing SDS The lane marked Input denotes total ci oss linked proteins prior to immunoprecipitation analysis Figure 5 A-C: W hile AU-nch element binding factoi s are important to promote RNA deadenylation and degi adation. the binding of the HuR protein to AU-nch elements is not associated with AU-nch element-mediated transcript instability Panel A Competition analysis suggests that AU-nch element binding factors are required for deadenylation and degradation of transcripts SVARE-A60 RNA was incubated in the in vitro stability system for 30 min in the presence of the indicated amounts of a svnthetic RNA competitor that contained the TNF-α AU-nch element (ARE comp ) oi a non-specific sequence RNA products were analyzed on a 5% acrylamide gel containing 7M urea The position of deadenylated SVARE-AO RNA is indicated Panel B. Reaction mixtures were prepared as described in panel A with the addition of EDTA to inhibit RNA turnover Protein-RNA interactions were analvzed by UV cross linking analvsis and analvzed on a 10% acrylamide gel containing SDS The positions of AU i ich element-specific cross linked species is indicated on the left Panel C. Reactions were prepared exactlv as described for Panel B. except samples were immunoprecipitated using a-HuR specific antisera prior to gel electrophoresis FIG. 6 A-D: ELAV piotems specifically stabilize deadenylated intermediates in the in vitro system Panel A. SVARE-A60 RNA was incubated in the in vitro svstem in the presence (lanes (+) Hel-N l )) oi the absence (lanes (-) Hel-N l ) ot l ug of recombinant Hel-N l protein RNA products wei e analvzed on a 5% acrylamide gel containing 7M urea The position of deadenylated SVARE-AO transcript is indicated Panel B. SVARE-A60 RNA was incubated in the in vitro svstem in the presence of l ug ot recombinant Hel-N l (lanes (+) Hel-N l ), GST only (lanes (+) GST) oi an unrelated RNA binding protein hnRNP H' (lanes (+) hnRNP H') RNA products were analvzed on a 5% acrv lamide gel containing 7M urea The position ot deadenvlated SVARE-AO transcript is indicated Panel C. ARE-A60 RNA or an unrelated transcript that lacked an AU- ch element (CX-A60) e incubated in the in vi o stability system for 30mιn in the presence (+ lanes) or absence (- lanes) of ~1 ug of Hel-N2 protein RNA products weie analvzed on a 5% aery lamide gel containing 7M urea The positions of deadenylated transcripts are indicated Panel D. A variant of S V-A60 RNA that contained the TNF-α ARE in the u' portion of the transcript ( SV5ΑGE-A60) was incubated in the in v ltro svstem tor 50 mm in the absence (- lane) or presence (+ lane) of 1 μg of Hel-N2 protein RNA products were analyzed on a 5% acrylamide gel containing 7 M urea The positions of imput and deadenvlated transcripts are indicated DETAILED DESCRIPTION OF THE INVENTION Numerous terms and phrases ai e used thi oughout the instant Specification The meanings of these terms and phrases are set forth below In particular, as used hei ein "half-life" of an RNA molecule refers to the measurement of the decline in the amount ot an RNA molecule to serve as a template for the synthesis of its protein product As used herein "turnovei ' refers to the degradation of an RNA molecule Turnover comprises deadenylation and degradation As used herein a cap or"5' cap oi terminal cap and be used interchangeable, and refer to a 7-methyl guanosine ( 7mG) cap chemical Iv conjugated to the most 5' nucleotide of the RNA molecule As used herein the phi ase "polvadenvlic acid (poly(A)) tail" l efers to a string of contiguous adenyhc acids ( poivadcnvlate) added post ti anscπptionallv to the 3' end of an RNA molecule, such as mRNA As used herein the tei m "stability" refers to the maintenance of an RNA molecule so that it can function and thus letard the degradation process ot an RNA molecule As used heiein. the phi ase "a polvadenvlic acid competitor nucleic acid oligomer" refers to an oligomer comprising contiguous adenylic acids" which can be added to a system of the invention and sequester proteins that bind poly(A) Thus, the degradation ot a particular RNA molecule having a poly(A) tail can be modulated Also, as used heiein the phrase lestπction endonuclease l efers to an enzvme that lecognizes specific nucleotide sequences in a nucleic acid molecule, and produces a double- stranded break w ithin or near the site Some restriction enzymes, such as £coRI or HindlU produce "complementary tails" on each of fragments pi oduced These tails are said to be "sticky" because under hybridization conditions they can reanneal with each other Thus, if two separate nucleic acid molecules share the same restπction site, then both will contain complementary single-stranded tails when tieated with the same restriction endonuclease. and can be spliced together foi ming a lecombinant nucleic acid molecule Naturally, as used herein the phrase "restriction endonuclease site" refers to a specific nucleotide sequence that is recognized by a specific resti iction endonuclease Furthermore, numerous conventional molecular biologv . microbiology, and recombinant DNA techniques within the skill ot the ait can be readilv utilized to practice the instant invention Such techniques are explained fullv in the literature See. e g , SambrooL Fritsch & Maniatis. Moleculai C loning A Laboratory Manual Second Edition ( 1989) Cold Spring Harbor Laboratory Press. Cold Spring Hai bor. New Yoi k (herein "Sambrook et al . 1989"), DNA Cloning f Practical Approach Volumes 1 and I I (D N Glover ed 1985). Ohgonitdeotide Svnthesis (M I Gait ed 1984) Nucleic Acid Hvbridi∑atmn [B D Hames & S J Higgins eds ( 1985 )] Ti anscripnon And T/ anslation [B D Hames & S J Higgms. eds ( 1984)], Animal Cell ( ulture [R I Freshnev, ed ( 1986)]. Immobilized Cells And Enzymes [IRL Press. ( 1986)], B Perbal, A Practical Guide To Molecular Cloning ( 1984), F M Ausubel et al (eds ), C urrent Protocols m Molecular Bιolog\ John Wiley & Sons. Inc ( 1994) Therefore, if appeal ing herein the following terms shall have the definitions set out below A "vector" is a rephcon. such as plasmid. phage or cosmid, to which another DNA segment may be attached so as to bring about the replication of the attached segment A "lephcon" is any genetic element (e g . plasmid. chromosome, virus) that functions as an autonomous unit of DNA replication in i ivo. i e . capable of l eplication under its own control A "cassette" refers to a segment of a nucleic acid molelcule, such as DNA or RNA, that can be inserted into a vectoi at specific l estπction sites The segment ot the nucleic acid molelcule mav encode a polv peptide of interest and the cassette and restriction sites are designed to ensui e insertion ot the cassette in the proper reading frame for transcription and translation A cell has been "transfected" bv exogenous or heterologous DNA when such DNA has been introduced inside the cell A cell has been 'ti ansformed" by exogenous or heterologous DNA when the transfected DNA effects a phenotvpic change Preferably, the transforming DNA should be integi ated (cov alently linked) into chromosomal DNA making up the genome ot the cell A "nucleic acid molecule" refei s to the phosphate ester polvmeπc form of πbonucieosides (adenosine. guanosine undine oi cvtidme "RNA molecules") or deoxynbonucleosides (deoxvadenosine deoxv guanosine. deoxythymidine. oi deoxycvtidine. "DNA molecules"), or any phosphoester anologs thereof, such as phosphorothioates and thioesters. in either single stranded form, oi a double-stranded helix Double stranded DNA-DNA. DNA-RNA and RNA-RNA helices are possible The term nucleic acid molecule, and in particular DNA oi RNA molecule l eters on lv to the primary and secondai v structure of the molecule and does not limit it to am particular tertiary forms Thus this tei m includes double-stianded DNA found, intei aha in lmeai or circular DNA molecules (e e . restriction fragments), plasmids, and chromosomes In discussing the structure of particular double-stranded DNA molecules, sequences may be desci ibed herein according to the normal convention of giving only the sequence in the 5 to 3 direction along the nontranscπbed strand of DNA (; e , the strand having a sequence homologous to the mRNA) A "recombinant DNA molecule" is a DNA molecule that has undei gone a molecular biological manipulation A DNA "coding sequence" is a double-stranded DNA sequence w hich is transcribed and tianslated into a polypeptide in a cell in vin or in vι\ o w hen placed under the control ot appropriate regulatorv sequences The boundaries of the coding sequence are determined by a start codon at the 5 ' (amino ) terminus and a translation stop codon at the 3 ' (carboxyl) terminus A coding sequence can include, but is not limited to, prokaryotic sequences. cDNA from eukaryotic mRNA. genomic DNA sequences from eukaryotic (e g , mammalian) DNA, and even synthetic DNA sequences I f the coding sequence is intended for expression in a eukaryotic cell a polyadenylation signal and transci iption termination sequence will usually be located 3 ' to the coding sequence A "promoter sequence ' is a DNA regulatoi v region capable of binding RNA polymerase in a cell and initiating transcription of a downsti eam (3 ' direction) coding sequence For purposes of defining the present invention, the promoter sequence is bounded at its 3 ' terminus by the transci iption initiation site and extends upstream (5 ' direction) to include the minimum number of bases or elements necessary to initiate transcription at levels detectable above background Within the promoter sequence will be found a transcription initiation site (conveniently defined for example, by mapping with nuclease S I ), as well as protein binding domains (consensus sequences ) responsible for the binding of RNA polymerase The present invention is based upon Applicant ' s discovery of a heretofore unknown system for activating regulated turnover of RNA molecules in i itro that surprisingly and unexpectedly pei mits a skilled artisan to study and to modulate the stability and thus the turnover of a RNA molecule m vitro Thus, the new and useful system of the invention permits accurate and faithful reproduction ot both general and regulated aspects deadenylation and degi adation of an RNA molecule, also referred to herein as recapitulating regulated RNA tui nov ei particularlv a eukai votic mRN A ti anscnpt In particular, the new and useful sv stem of the invention permits m inimal amounts pi eferably undetectable. of mRNA turnov er, and fui thei . deadenylation ot an RNA molecule occurs in the svstem prior to degradation ot the RNA molecule, which mimics the turnovei process of RNA found in The kev to the dev elopment of the svstem and methods utilizing the system are based on the discoverv that polvadenvlate competitor RNA is capable ot sequestering proteins that bind polyadenylate and consequently activating the deadenv lase enzyme, inducing RNA turnover As it was heietofore considered that such proteins that bind polyadenylate may contribute to RNA deadenylation. the present finding that such proteins are. in contrast, stabilizers of RNA, led to the l eahzation that the such pi oteins are interacting with and inactivating destabilizing mediatoi s in vivo Thus, the present invention is directed to an in vitro system capable of recapitulating regulated RNA turnover of an exogenously added preselected target RNA sequence comprising a cell extract depleted of activity of proteins that bind polyadenylate. and a pi eselected target RNA sequence In one particular embodiment, the l egulated RNA turno er is that modulated bv AU-nch element (ARE) regulated RNA turnover Examples ot mRNAs with AU-i ich elements include those of. by way of non- limiting example, c-ios. c-)un. c-myc TNF-α. GMCSF. IL l - 15, and IFN-β A.s noted above. AU-nch elements are sites tor binding of numerous proteins, including the ELAV family of ARE-binding proteins, such as HuR . Hel-N l HuC and HuD, others include AUF1. tπstetrapolin. AUI I. HA TIAR glvceιaldehvde-3-phosphate. hnRNP C. hnRNP A l , AU-A. and AU-B In anothei embodiment the l egulated RN A turnover is that modulated by C-nch element (CRE) legulated RNA turnover such elements as found in the mRNA of globin mRNAs, collagen, ltpoxygenase. and tv l osine hydioxvlase Another mRNA with an as yet uncharacteπzed sequence element is that ot VEGF The invention, however, is not so limiting as to the particular elements or binding proteins to these elements involved in the regulation of RNA turnover The cell extract ot the pi esent invention is prepared from lysed eukaryotic cells or tissues Various methods kno n to the skilled artisan may be used to prepai e the cell extract Various sources of cells mav be used, including fresh cells and tissues, and cells lines Such cells mav comprise foieign nucleic acid, such as in cells that are infected, or are transiently oi stablv transfected w ith a mammalian expiession vector the latter as descnbed in more detail below For certain purposes, tor example to investigate the role of infection, and in particular lntracellulai infection, on RNA turnover, infected cells may be utilized as the source of the cell exti act herein Cells infected with vn uses or other intracellular microorganisms such as Liberia monocvtogenes. HTLV herpes simplex virus, and HIV, may be employed foi these particular circumstances Furthermore, prior to preparation of the cell extract, cells may be exposed to certain chemical or other extracellular stimuli, for example, hormones, growth factors and kinase and phosphatase inhibitors which mav alter RNA turnover, for which subsequent studies as described herein may be used to identify the induction of certain proteins involved in modulating RNA turnover, or for the identification of agents which may counteract adverse RNA turnovei modulation induced by such stimuli As will be noted in moie detail below, the methods herein may be used to identify agents which may protect ceils by interfering with adverse RNA turnover induced by various sources The cell exti act is preferablv free of nuclei and nuclear contents and comprises cytoplasm, but this is not essential unless particular components, such as enzymes oi other factors, from nuclei, interfere with the opeiation of the svstem In a typical preparation, which may be modified without departing fi om the scope ot the invention, cells are grown, harvested, lysed. centi ifuged foi 100.000 x g tor 1 hoiii . and dialvzed Glycerol may be added to protect the exti act if stored frozen As described abov e. a cell used to prepare the cell extract mav comprise foieign DNA An isolated nucleic acid molecule to placed in a system of the invention can initially be inserted into a cloning vector to produce numerous copies of the molecule A large number of vector- host systems known in the art may be used Possible v ectors include, but are not limited to. plasmids or modified v n uses. but the ectoi system must be compatible with the host cell used Examples ot vectors include, but are not limited to E coh. bactenophages such as lambda derivatives, oi plasmids such as pBR322 derivatives or pUC plasmid derivatives. e g , pGEX vectors, pmal-c, pFLAG. etc. The insertion into a cloning vector can, tor example, be accomplished by hgating the nucleic acid molecule into a cloning vector which has complementary cohesive termini However, if the complementary restriction sites used to fragment the nucleic acid molecule are not present in the cloning vector, the ends of the molecule may be enzymaticaily modified Alternativelv . any site desired may be produced by hgating nucleotide sequences (linkers) onto the termini of the nucleic acid molecule, these ligated linkers mav comprise specific chemically synthesized oligonucleotides encoding restriction endonuclease lecognition sequences Recombinant molecules can be introduced into host cells via ti anstormation. ti ansfection. infection electroporation. etc . so that many copies of the nucleic acid molecule are generated Preferably, the cloned nucleic acid molecule is contained on a shuttle vector plasmid. which provides for expansion in a cloning cell, e g . E coh. and facile purification for subsequent insertion into an appropriate expression cell line, il such is desired For example, a shuttle vector, which is a vector that can replicate in more than one type of oi ganism. can be prepared for replication in both E .11- coh and Saccharomvces cerevisiae bv l inking sequences ti om an E co plasmid with sequences from the yeast 2μ plasmid Naturally, any of the methods previously described for the insertion of an isolated nucleic acid molecule into a cloning vector may be used to construct expression vectors containing a nucleic acid molecule consisting of appropπate transci lptional/translational control signals and the protein coding sequences These methods mav include in vitro recombinant DNA and synthetic techniques and in vivo recombination (genetic recombination) Mammalian expression vectors contemplated for use in the invention include vectors with inducible promotei s. such as the dihvdrofolate reductase (DHFR) promoter, e g , any expression vector with a DHFR expression vector, oi a Zλf FR/methotrexate co-amplification vector, such as pED (Atl. Sail. Sba\. Sma\. and EcoRI cloning site, with the vector expressing both the cloned gene and DHFR. see Kaufman, Current Protocols in Molecular Biology, 16 12 ( 1991 ) Alternatively, a glutamine synthetase/methionine sulfoximine co- amphfication vector, such as pEE14 (Hindlll. Xbal. S al, Sbal. EcoRI. and Bell cloning site, in which the vector expresses glutamine svnthase and the cloned gene. Celltech) In another embodiment, a vector that directs episomal expression under control of Epstein Barr Virus (EBV) can be used, such as pREP4 (BamH 1. Sfή. Xhol. Not\. Nhel. Hindlll, Nhe . Pvulf and Kpnl cloning site, constitutive RSV-LTR pi omoter. hygromycin selectable marker, Invitrogen), pCEP4 (BamH l . Sfil. Xhol. Noll. Nhel. Hindlll. Nhel. Pvull. and Kpnl cloning site, constitutive hCMV immediate early gene, hygromvcin selectable marker, Invitrogen), pMEP4 (Kpnl. P\ u . Nhel. Hindlll. Noll. Xhol. Sfil. BamH l cloning site, inducible metallothionein Ha gene promoter, hygromycin selectable marker Invitrogen). pREP8 (BamH l . Xhol. Not . Hindlll \ hel. and Kpnl cloning site. RSV-LTR promoter, histidinol selectable markei iti ogen ). pREP9 (Kpnl λ el. Hindl ll Nυtl. Xhol. Sfil. and BamHl cloning site. RSV-LTR promoter. G4I 8 selectable marker. Invitrogen). and pEBVHis (RSV- LTR promoter, hy gromycin selectable markei N-termmal peptide punfiable via ProBond resin and cleaved by enterokmase. Invitrogen ) Selectable mammalian expression vectors for use in the invention include pRc/CMV (Hindl ll. BstX \otl. Sbal. and Apal cloning site. G418 selection. Inviti ogen). pRc/RSV (Hindlll. Spel. BstXl. Notl. Xbal cloning site, G418 selection. Invitrogen). and others Vaccinia virus mammalian expression vectors (see, Kaufman. 1991 supra) tor use according to the invention include but are not limited to pSCl 1 (Smal cloning site, TK- and β-gal selection). pM 1601 (Sail. Sma , Afll, Nar , BspMll. BamHl. Apal. Nhel, Sac ll, Kpnl and Hindi 11 cloning site TK- and β-gal selection), and pTKgptF l S (£ oRI A/I Sail. 4ccl. Hindl l Sbal. BamHl. and Hpa cloning site. TK or XPRT selection) Once a particular nucleic acid molecule, such as RNA is inserted into a vector, several methods known in the art mav be used to pi opagate it Once a suitable host system and gi owth conditions are established, recombinant expression vectors can be propagated and prepared in quantity As previously explained, the expiession vectors which can be used include, but are not limited to. the following vectors or their derivatives human or animal viruses such as vaccinia virus or adenovirus insect viruses such as baculovirus. yeast vectors, bactenophage vectors (e g . lambda), and plasmid and cosmid DNA vectors, to name but a few In addition a host cell sti ain mav be chosen w hich modulates the expression of the inserted sequences or modifies and processes the gene product in the specific fashion desired Vectors are mtioduced into the desu ed host cel ls bv methods know n in the art. e g . transfection. electropoiation. mιcroιn|ectιon tiansduction. cell fusion, DEAE dextran. calcium phosphate pi eαpitation hpofection ( lysosome fusion) use of a gene gun. or a DNA vector transporter (see a g , Wu et al . 1992, J Biol Chem 267 963-967. Wu and Wu, 1988. J Biol Chem 263 14621 - 14624. Hartmut et al . Canadian Patent Application No 2.012.31 1. filed March 1 5. 1990) Cells useful for the preparation described herein include immortalized or partiallv immortalized cells which can be grown in lai ge amounts under defined conditions, such as HeLa cells and vai ious T-cell cell lines Other sources include tissues, blood cells, or myeloid cells Other soui ces ai e well within the realm of the present invention The cell extract ot the svstem descnbed herein is depleted of activity of proteins that bind polyadenylate This mav be achieved by anv one or a combination of methods such as the following While not being bound by theorv . each of these methods either removes the proteins that bind polyadenylate. or inactivate the binding activity These procedures may be applied to the cel l exti act as it is used in the methods described herein, or the cell extract may be treated beforehand Tor example, a polv adenvlate competitor RNA may be added to the cell extract to provide an irrelevant RNA sequence to which the binding proteins may bind. thus clearing the target RNA sequence of such binding proteins In another embodiment, sequestration of proteins that bind polyadenylate mav be performed Sequestration may be achieved by adding to the cell extract or exposing the cell extract to a material that binds the aforementioned proteins, such as antibodies to piotems that bind polyadenylate. or polyadenylate sequences themselves or macromolecules comprising polyadenylate sequences which serve as binding targets tor such proteins Altei natively or in addition, these protein binding matenals mav be bound to a matrix such as agai ose beads, and the cell extract passed through a column of such beads to l emove the pi oteins which bind polyadenylate The preparation of such beads covalently modified to comprise antibodies 01 RNA sequences, whether polyadenylate or sequences comprising polyadenylate. are known to the skilled artisan Anothei means for reducing 01 eliminating such activity from the cell extract is by exposure to one 01 more proteinase known to inactivate a piotein that bind to polyadenylate These proteinases may be added to the extract, or bound to a matrix and exposed to the extract, after which inactivation the beads may be removed A further means encompasses addition to the extract of an agent that prevents the interaction between polyadenylate and an endogenous macromolecule that binds to polyadenylate These and other methods embraced bv the present invention achiev e the desired goal of depleting macromolecules that bind polyadenylate ti om the cell extract, thus allowing the cell extract in combination w ith the target RNA sequence to undergo in vivo-bke RNA turnover One or a combination of the atoi esaid methods may be employed to reduce the level of such protein to an acceptable limit dependent upon the source of the cells or tissues from which the extract is made, the particular target RNA sequence, and other factors As will be noted below certain macromolecules that bind to polyadenylate may be mcluded in particulai screening assays or other methods employing the system and methods described herein when that particular protein or other macromolecule is subject to investigation as described herein In a further embodiment of the invention, the cell extract may be partially purified or otherwise manipulated or example, the cell extract may be partially purified to remove certain components betoi e being placed in the system of the invention, before or after being optionally depleted ot macromolecules that bind polyadenylate For example, certain non- specific factors and/oi activities unrelated to of interfei ing ith the methods of the present invention may be removed from the cell exti act The skilled artisan will recognize for the particular target RNA being investigated hei eundei the need toi partial purification of the extract and the need toi depletion of factoi s that bind polvadenv late Furthermore, other components may be added to ensure that the system ot the inv ention recapitulates regulated RNA turnover The target RNA sequence in the system of the present invention may be an one of a number of RNA or modified RNA molecules For example, synthetic RNA may be prepared by solid phase synthesis, or reproduced by in vitro transcription using phage polymerase as is known to the skilled artisan Naturally occurring RNA may be isolated from cells, tissues, and other biological sources The RNA may be a messenger RNA (mRNA), a preferred species herein, or RNA-DNA derivatives Messenger RNA typically comprises a 5' cap and a 3' polyadenylate sequence Chemically modified RNA. such as RNA modified by phosphothioate moιety( ιes), is embraced herein The particular RNA. including mRNA, used in the system and methods of the present invention may be selected depending on the particular species of mRNA to be studied Investigations of mRNA turnover, endogenous modulators of its turnover and exogenously added molecules, particularly small molecules which affect mRNA turnover, have important therapeutic implications in the prophylaxis and treatment of a variety of conditions and diseases Certain mRNAs are short-lived, such as those of cytokines, others are long-lived, such as globin message The regulation of mRNA lifetimes for particular proteins and particular cell types may be sub)ect to various adverse effects, ti om infection to external stimuli, which alter the turnover and hence cellular physiology in various conditions, altered expression of cellular proteins and cellular phenotypes mav be consequences of altered mRNA turnover. Pharmacological intervention of such altered mRNA turnover, to restore an altered turnover, or the induction of an altered turnover to achieve a benefit to the organism, are achievable based upon the systems and methods described herein. For example, a particular mRNA. such as that of the proinflammatory cytokine TNFα. is selected as a target for identification of small molecule modulators that may decrease the turnover, and this prolong the lifetime, and expression, of this protein by inflammatory cells. Such modulators may provide substantial benefit in the treatment of certain immunological diseases wherein an increased secretion of TNFα is beneficial. Conversely, massive overproduction of TNFα in sepsis, or its adverse effects in rheumatoid arthritis and inflammatory bowel disease may be ameliorated by use of an agent which further increases the turnover ands thus decreases the expression of TNFα by inflammatory cells. The application of the invention herein to other mRNA species is embraced by the teachings herein. In particular, the methods of the present invention facilitate high throughput screening for the identification of modulators of RNA turnover, to be applied to the treatment or prophylaxis of disease. One aspect of the system and method of the present invention is monitoring the turnover of the target RNA sequence. This may be achieved by any one or a combination of various methods known to the skilled artisan, one of which is the provision of labeled RNA. The target RNA sequence of the present may be unlabeled. labeled, or a combination. For example, after setting up conditions under which the deadenylation and/or degradation of the unlabeled target RNA sequence occurs, its level may be assessed by any of a number of methods utilizing a labeled probe, such as by hybridization, or by way of UV absorbance, gel electrophoresis followed by specific or nonspecific staining, or using an amplification system, such as phage polymerase. and then quantitation by a suitable amplification-based technique such as the molecular beacon method Altei natively, and perhaps more simply, the target mRNA sequence may be labeled, and the extent ot intact sequence oi degraded RNA fragments readily quantitated Labels such as a fluorescent moiety, a visible moiety, a ladioactive moiety , a ligand, and a combination of fluoi escent and quenching moieties These non-limiting examples are provided for purposes of illustration only Furthermore, optionally, an RNA molecule or a portion thereof, such as its poly(A) tail, may be detectably labeled using routine protocols readily known to a skilled artisan Suitable labels include enzvmes. fluorophores (e g . fiuorescem isothiocvanate (FITC). phvcoerythrin (PE). Texas red (TR) i hodamine, free or chelated lanthanide series salts, especially Eu + , to name a few fluorophores). chiomophores. l adioisotopes chelating agents, dyes, colloidal gold, latex particles, ligands (e g , biotin). and chemiluminescent agents When a control marker is emploved. the same or different labels may be used for the receptor and control marker In the instance where a tadioactive label, such as the isotopes 'H. M C, 32 P. "S, 16 C1, "Cr, 37 Co, 38 Co, "''Fe, 90 Y. ι : 4 m I. and l 8b Re are used, known currently available counting procedures may be utilized Particular πbonucleotides bay be prepared using the appropriate isotopes, and the labeled RNA pi epared by solid phase synthesis Alternatively, moieties comprising the isotopes may be covalently bound to the RNA In the instance where the label is an enzyme, detection mav be accomplished by any of the presently utilized coloπmetπc. spectrophotometπc. fluoiospectrophotometπc, amperometπc or gasometπc techniques known in the ait I n a turther example, biotm moieties may be incorporated into the RNA by any number of means. Subsequently, the biotinyiated RNA or degradation fragments may be quantitated by an avidin reagent. Direct labels are one example of labels which can be used according to the present invention. A direct label has been defined as an entity, which in its natural state, is readily visible, either to the naked eye. or with the aid of an optical filter and/or applied stimulation, e.g. U.V. light to promote fluorescence. Among examples of colored labels, which can be used according to the present invention, include metallic sol particles, for example, gold sol particles such as those described by Leuvering (U.S. Patent 4.3 13,734); dye sole particles such as described by Gribnau et al. (U.S. Patent 4.373,932) and May et al. (WO 88/08534): dyed latex such as described by May. supra, Snyder (EP-A 0 280 559 and 0 281 327); or dyes encapsulated in liposomes as described by Campbell et al. ( U.S. Patent 4,703,017). Other direct labels include a radionucleotide. a fluorescent moiety or a lum inescent moiety. In addition to these direct labelling devices, indirect labels comprising enzymes can also be used according to the present invention. Various types of enzyme linked immunoassays are well known in the art, for example, alkaline phosphatase and horseradish peroxidase, lysozyme, glucose-6- phosphate dehydrogenase. lactate dehydrogenase. urease. these and others have been discussed in detail by Eva Engvall in Enzyme Immunoassay ELISA and EMIT in Methods in Enzγmology, 70. 419-439. 1980 and in U.S. Patent 4.857,453. Suitable enzymes include, but are not limited to. alkaline phosphatase and horseradish peroxidase. Other labels for use in the invention include magnetic beads or magnetic resonance imaging labels. As noted herein, turnovei of RNA occurs in two steps deadenylation, which is not dependent upon the presence of nucleotide tπphosphates. and degi adation. which is so dependent The level of nucleoside tπphosphates. including l ibonucleotide and/or deoxyπbonucieotide tπphosphates. A FP L' I P. CTP TTP. and/oi GTP. in the cell extract may 01 may not be sufficient to permit the degradation aspect ot RNA tui novei to occur In one embodiment of the present invention, the system described herein additionally comprises exogenously added nucleotide tnphosphate. preferably ATP. It was noted during the development of the present invention that the inclusion of a reaction enhancer resulted in a slight stimulation in the efficiencv of RNA degiadation This is likely to be due to its ability to promote macromolecular complex formation in vitio Therefore, the invention herein optionally includes the use of a reaction enhancer such as a polymer, to stimulate interaction among the components of the system Non-limiting examples include polyvinyl alcohol, polvvinylpyrrohdone and dextran, polyvinyl alcohol is preferred The above-described sv stem which recapitulates in viti o the RNA turnover of preselected RNA sequences has sev eral utilities, in particular, the identification of the role of endogenous factors and exogenous modulators in RNA turnovei The present invention is broadly directed to a method toi identifying an agent capable ot modulating the stability of a target RNA sequence comprising (A) prepai ing the system as described hereinabove. (B) introducing said agent into said system (C) determ ining the extent of tui novei of said target RNA sequence, and (D) identity ing an agent able to modulate the extent of said turnover as capable ot modulating the stabilitv ot said target RNA sequence The above method mav additionally comprise added nucleotide tnphosphate. preferably ATP. for the purposes described above Agents whose activitv in modulating RNA turnover mav de detected in the aforementioned method include but is not limited to an RNA stability modify ing molecule As described abov e, the target RNA sequence mav be selected as described above, depending on the particulai RNA to be studied The tai get RNA may be unlabeled target RNA sequence, labeled target RNA sequence. 01 the combination thereof Labels include but are not limited to a fluoiescent moiety, a visible moiety, a l adioactive moiety, a ligand. or a combination of fluorescent and quenching moieties The monitoring the extent of turnover of said target RNA sequence comprises determining the extent of degradation of said labeled tai get RNA, bv the methods described above In particular, the present method may be dn ected to identifying agents capable of modulating the stability of a target RNA sequence which increases the stabilitv of the target RNA sequence, or alternatively, deci easing the stability of the RNA sequence In a particular embodiment, the agent is capable of modulating the activity of a AU rich element binding protein or a C-nch element, but it is not so limited Examples of AU rich element binding proteins and C-πch element binding proteins are as described herein In a further embodiment of the present invention, a method is provided for identifying an agent capable of modulating the stability ot a target RNA sequence in the presence of an exogenously added RNA stability modifier comprising (a) preparing the system as described hereinabove. (b) introducing said RNA stability modifiei into said system. (c) introducing said agent into said system (d) determining the extent of turnover of said taiget RN A sequence, and (e) identifying an agent able to modulate the extent of said turnover as capable of modulating the stability ot said target RNA sequence in the presence of said exogenouslv added RNA stability modifier This aspect of the invention is directed to identifying agents, in particular small molecules, capable of affecting the activity of a RNA turnover modulator As described above, such small molecules may be screened to determine their effect on the RNA stabilizing or destabilizing ability of an endogenous mediator which is added to the test system Alternatively, it mav be used to identify compounds w h ich agonize or antagonize exogenous agents The components of the svstem including nucleotide tnphosphate. the target RNA, labels, are as described above In one aspect of this embodiment, the RNA stability modifier increases the stability of said target RNA sequence, and in a further embodiment, the agent decreases the stability of said target RNA sequence inci eased by said RNA stability modifier In another embodiment, the RNA stability modifier decreases the stability of said target RNA sequence, and in a further embodiment, the agent increases the stability of said target RNA sequence decreased bv said RNA stability modifier -j j- Candidate series ot RNA stability modifiei s include the AU rich element binding proteins, but the invention is not limited to such factoi Examples ot known proteins having such elements in the mRNA. and binding proteins to the elements, are described above, however, the invention is not lim ited to these examples Furthermore, in anothei embodiment, the macromolecules that bind RNA that are removed from the cell exti act in accordance with the aforementioned procedures may be added back to the system herein to investigate their role in RNA turnover as well as the effect of agents, in particular small molecules, on RNA turnover modulated by these macromolecules that bind RNA This embodiment may be applied to any of the methods described herein In yet another embodiment, the target RNA may be loaded with a macromolecule that binds RNA prior to addition to the system herein, for the same purposes stated above As noted above, the cell extract used in any of the methods described herein may be partially purified A method is also provided for identifying an agent capable of modulating the deadenylation of a target RNA sequence comprising (A) pieparmg the svstem of the present invention in the absence of a nucleotide tnphosphate, (B) introducing said agent into said system, and (C) monitoi g the deadenylation of said target RNA sequence in said system A further method is pi ovided foi identifying an agent capable of modulating the deadenylation and degi adation of a target RNA sequence comprising (A) piepai ing the svstem of the pi esent inv ention in the presence of ATP, (B) introducing said agent into said system and (C) monitoi mg the deadenylation and degiadation ot said target RNA sequence in said system Method are also provided herein for identity g an agent capable of modulating cell growth or cell differentiation in a mammal comprising determining the ability of said agent to modulate the stability ot a target RNA sequence involved in the modulation of cell growth or differentiation, utilizing the aforementioned methods The agent capable of modulating cell growth or cell differentiation may intervene in cellulai transformation, or in immune dysregulation A further embodiment ot the present invention is directed to a method for identifying, characterizing or isolating an endogenous molecule suspected of participating in the deadenylation or degi adation of RNA or regulation thereof comprising (A) prov iding the svstem of the present invention as described above. (B) introducing said protein suspected of participating in the regulation of RNA turnov ei into said system. (C) monitoi mg the stability of said target R A sequence in said system, and (D) identifying, characterizing or isolating said endogenous molecule able to modulate said deadenylation or degradation as capable of participating in the deadenvlation or degradation of RNA or regulation thereof The molecule suspected of participating in the deadeny lation or degradation of RNA or regulation thereof may be protein or RNA In another embodiment of the present invention, a method is provided for identifying an agent capable of modulating the degradation a tai et RNA sequence in the absence of deadenylation comprising (A) providing a cell extract in the presence ot a nucleotide tnphosphate, (B) introducing said agent into said cell extiact. and (C) monitoring the degradation of said target RNA sequence in said extract The present invention is also directed to kits for monitoring the stability ot a preselected target RNA sequence under conditions capable ot recapitulating regulated RNA turnover Such kits comprise (a) cell extract optionally depleted of activity of proteins that bind polyadenylate. (b) other i cagents. and (c) directions for use of said kit A kit may further comprising nucleotide tπphosphates a reaction enhancer, a target RNA sequence. RNA binding proteins. RNA stability modifiei s. or any combination thereof It will be seen by the skilled artisan that the kits of the invention provide the components for carrying out the various methods disclosed herein, such as identifying agents and endogenous factors that modulate RNA turnover identifying agents which modulate the RNA turnover activity of various factors involved in RNA turnover, and others, in particular use in the screening of small molecules tor identifying potentially useful therapeutic agents for the prophylaxis and/or treatment ot various conditions or diseases benefitted by modulating RNA turnover The kits mav be prepared to investigate either RNA deadenylation. RNA degradation, or both, depending on the components as described above Furthermore, the cell extract may be partially purified I he kit may include i cagents tor depleting activity of proteins present in the extract which bind polyadenylate. such reagents, such as polyadenylate. polyadenylate bound to a matrix, an antibody to proteins that bind polyadenylate, and such an antibody bound to a matrix The present invention may be bettei understood by refei ence to the following non-limiting Examples, which are pi ovided as exemplai v of the invention The following examples are presented in order to moi e fully illustrate the preferred embodiments of the invention They should in no way be construed, however, as limiting the broad scope of the invention. EXAMPLE I ELAV Proteins Stabilize Deadenylated Intermediates in a Novel In Vitro mRNA Deadenylation/Degradation Svstem Set forth herein is a novel in vitro mRNA stability system using Hela cell cytoplasimc S I 00 extracts and exogenous polyadenvlated RNA substrates that reproduces regulated aspects of mRNA decay (turnovei ) The addition ot cold poly(A) competitor RNA activated both a sequence-specific deadenvlase activity in the extracts as well as a potent. ATP-dependent nbonucleolytic activity The rates of both deadenylation and degradation were up-regulated by the presence ot a variety of AU-nch elements in the body of substrate RNAs. Competition analyses demonstrated that trans-a.cX.mg factors were required for RNA de-stabilization by ΛU-i ich elements The -30 kDa ELAV protein, HuR. specifically bound to RNAs containing an AU-nch element denved from the TNF-α mRNA in the in vitro system Interaction ot HuR with AU-nch elements, however, was not associated with RNA destabilization Interestingly. l ecombinant ELAV proteins specifically stabilized deadenylated intermediates generated from the turnovei ot AU-nch element-containing substrate RNAs Thus, mammalian ELAV proteins plav a role in regulating mRNA stability by influencing the access of degradative enzvmes to RNA substrates The relative stability oi mRNA is an important regulatoi of gene expression The half-life of a specific mRNA can play a role in determining both its steady state level of expression, as well as the rate at which its gene product is induced (reviewed in Ross, 1995, Caponigro and Parker. 1996) Furthei more. mutations that affect the stability of mRNAs encoding regulatory factors can pi omote oncogenic tianstormation and immune dysregulation (Aghib et al . 1990, Schiavi et al , 1992) In general, many short-lived proteins, including those derived from cytokines and proto-oncogenes. are encoded by short-lived mRNAs Several mRNAs that encode stable proteins, such as a-globin. have also been shown to have extraordinarily long half-lives (Holcik and Liebhaber. 1997) In addition, surveillance mechanisms that identify and reduce the half-lives of aberrant mRNAs that contain nonsense codon mutations have been described (Maquat. 1995. Jacobson and Peltz, 1996) Therefore, regulation ot the half-li fe of mRNAs can have diamatic consequences on cellular responses and functional outcomes during growth and development Through the application of genetics, the mechanisms and factois involved in the turnover of mRNA in Saccharomvces cerevisiae are beginning to be identified Multiple pathways of mRNA turnover are present in yeast, allowing foi numei ous levels of regulation and fine-tuning of gene expi ession One genei al pathway ot mRNA decay involves poly(A) tail shortening followed bv decapping and 5'-to-3 exonucleolytic decay (Muhlrad et al , 1994) A second general pathway involves deadeny lation followed by 3 " -to-5 * turnover of the body of the mRNA (Anderson and Parker. 1998) Endonucleolvtic cleavage of some mRNAs has also been demonstrated (Presutti et al . 1995) Finally another alternative decay pathway that bypasses deadenv lation is involv ed in the ti anslation-dependent degradation of nonsense codon-containing mRNAs (Weng et al , 1997) Sevei al degradation enzymes and regulatory proteins that play a role in mRNA stability in yeast hav e been identified (Caponigro and Parker, 1996. Weng et al . 1997) Functionally significant interactions between the cap structure and the 3 polv(A) tail of yeast mRNAs have also been described (Tarun and Sachs, 1997) Whether these observations are generally applicable to mammalian cells, however, remains to be established In vivo observations ai e beginning to allow some generalizations concerning major pathways of mRNA turnover in mammalian cells A poly(A) tail of approximately 200 bases is added to most mRNAs during processing m the nucleus (Colgan and Manley, 1997) The poly(A) tail serves at least two known functions in mRNA stability First, in association with poly(A) binding proteins (Bei nstein et al , 1989, Toi d et al . 1997), it protects the mRNA from 3'-to-5 " exonucleases Second, the poly(A) tail serves as an initiation site for the turnover of the mRNA The pol (A) tail can be progressively shortened throughout the lifetime of a mRNA in the cytoplasm Controlling the l ate of deadenvlation appears to be an important regulatory point in mR A. stability ( Wilson and Treisman, 1988. Xu et al . 1997) Once the poly(A) tail is shortened to approximately 30-65 bases, the body of the mRNA appears to be degraded in a rapid fashion in vivo without the accumulation of discernible intermediates (Chen et al . 1995. Xu et al , 1997) Little is known, however, concerning the enzymes and legulatory components involved in mammalian mRNA turnover In addition to the poly( Λ) tail, sevei al ezs-actmg elements hav e been shown to play a role in mRNA stability The 5 terminal cap structure protects the transcript from exonucleases (Furuichi et al.. 1977) Several destabilizing elements ( Caput et al . 1986: Shyu et al., 1989; Bonnieu et al., 1990: Peng et al.. 1996), as well as stabilizing elements (Stefonovic et al., 1997). located in the body of the mRNA have also been identified One well-characterized element that regulates mRNA stability is an AU-rich sequence (ARE) found in the 3 ' untranslated region of many short-lived mRNAs (Shaw and Kamen. 1986). These AREs primarily consist of AUUUA repeats or a related nonameπc sequence (Lagnado et al., 1994, Zubiaga et al.. 1995: Xu et al.. 1997) and have been divided into three classes based on sequence characteristics and degradation kinetics ( Xu el al . 1997) In general. AREs have been shown to increase the rate of deadenylation and RNA turnover in a translation-independent fashion (Chen et al . 1995; Fan et al.. 1997) The underlying mechanism behind ARE function, howevei . remains to be determined Numerous proteins have been described that can bind in vitro to AU-nch elements (e.g. Maker, 1989: Vakalopoulou et al.. 1991 : Bohjanen et al , 1991 ; Brewer. 1991 ; Levine et al., 1993: Hamilton et al . 1 993; Katz et al.. 1 94. Nakagawa et al , 1995: Ma et al , 1996), but the exact role of each factor in the process ot mRNA tin nover remains to be defined. The ELAV family of ARE-binding proteins is evolutionaπlv conserved and differentially expressed in tissues throughout the development of vertebrates (reviewed in Antic and Keene. 1997) Although ELAV proteins have been found m both the cytoplasm and the nucleus (Gao and Keene. 1996). the most ubiquitously expressed form. HuR. can shuttle between the nucleus and the c toplasm (Fan and Steitz. 1998: Peng et al., 1998; Atasoy et al. 1998). ELAV proteins play an important l ole in growth and development, as the Drosophila homolog is genetically essential for development and maintenance of the nervous system (Campos et al , 1985 Robmow and White 1988) In addition, mammalian ELAV proteins are induced during differentiation and are distributed in RNP granules along dendπtes (Gao and Keene. 1996) Sev ei ai lines of evidence suggest that ELAV proteins control aspects ot post-transcπptional gene expression (Gao and Keene 1996 Kousluka et al . 1996. Myer et al , 1997. Ma et al , 1997 Antic and Keene. 1998) 0\ eι -expression of ELAV family members, for example, has been shown to affect accumulation of selected mRNAs (Jain et al , 1997. Levy et al . 1998, Fan and Steitz. 1998. Peng et al . 1998) The precise role of ELAV proteins and other ARE-binding factors, howevei . remains to be established Mechanistic questions in mammalian cells ai e usually best approached using biochemical systems due to the inhei ent difficulties with mammalian cells as a genetic system It has been difficult, howevei to establish a v ersatile in vitro svstem to study mRNA stability and turnover Based on //; i ivo observations and practical considerations, an optimal in vitro system to study the process of mRNA stability should have the following properties First. the system should be efficient and highly reproducible Second, minimal amounts (preferably undetectable) of RNA degradation in the sv stem should be due to random degradation by non-specific contaminating πbonucleases Third, deadenylation should occur before general degradation of the mRNA bodv is observed Fourth, degradation of the mRNA body should occur in an apparently highly processive fashion without detectable intermediates Fifth, l egulation of the rate of overall deadenylation and degradation should be observed in a sequence-specific manner Finally, the system should work on exogenous RNAs to allow ease of experimental manipulation Reported herein is the discovery ot a new and useful m \ πro mRNA stability system using cytoplasmic S 100 exti acts that fulfills all of the criteria listed above and possesses all of the properties known to be involved in ARE-mediated mRNA turnover This system has been successfully used to demonstrate a role for the AU-nch element binding proteins of the ELAV family in mRNA stability These findings indicate that ELAV proteins can affect a default pathway of ARE-mediated degradation by either protecting the mRNA from nuclease attack or by displacing factors that otherwise mark these short-lived transcripts for degradation This in vitro system allows the identification of cellular factors involved in mRNA turnover and help elucidate mechanisms involved in the post-transcπptional regulation of gene expression Moreover, the in vitro system of the invention has readv applications in high throughput assays to sci een libraries of compounds to elucidate which compounds may have applications as pharmaceuticals which can modulate the stability and turnover of RNA transcripts in vivo. and thus be used to tieat a wide variety of disease or disorders l Development of an /;/ vitro Svstem that Deadenylates and Degrades RNA Substrates The development of an in vitro system to study mRNA turnover requires the generation of a convenient source of polv( A) RNA substrate and an active cellular extract In order to obtain substrate RNAs that were both polyadenylated and easy to identify using standard acrylamide gel technology, a novel and vei satile ligation-PCR approach that can attach a template encoding a 60 base poly(A) tail to the 3 n end of DNA fragments that contain a Hind III site was used, and is described infra In initial studies to develop an in vitro RNA stability system, a 60 base poly(A) tail was attached to a 54 base polylinker-denved sequence (Gem-A60) The small size of this polyadenylated transcript made it easy to analyze intermediates in the pathway of RNA turnover on acrylamide gels Cellular extracts were prepared following a standard cytoplasmic S I 00 protocol (Dignam et al . 1983) using hypotonicallv lysed Hela spinner cells with minor variations as described in the Materials and Methods Gem-A60 RNA w as incubated in S I 00 extracts in the pi esence ot ATP As seen in Fig 1 A (left panel), verv little tui novei of the Gem-A60 RNA as noted after 60 minutes of incubation This repioducible slow rate of turnover prompted us to hypothesize that an inhibitor of the deadenvlation/degradation process might be present in S I 00 extracts This hypothesis was based on several observations First, pi evious work with nuclear extracts determined that poly(A) binding pioteins wei e strong inhibitors of a 3 " -to-5 exonuclease activity (Ford et al 1997) Second the activity of a partially purified mammalian deadenylase preparation was inhibited bv h igh amounts ot PABP (Korner and YΛ able, 1997) Third, over-expression of PABP in Xenopus oocytes inhibits maturation-specific deadenylation (Wormington et al . 1996) In order to test whether excess amounts of poly(A) binding proteins were lesponsible for inhibiting the deadenylation of Gem-A60 RNA in S I 00 extracts, increasing amounts of cold poly(A ) competitoi RNA were added to the reaction mixtures to sequester poly(A) binding proteins As shown in Fig 1 A (right side) the addition of poly(A) competitoi activated a degradation activity in the S I 00 extracts The Gem-A60 RNA was shortened to a species slightly larger than the size of a deadenylated marker (Gem-AO) and approximately 30% of the input RNA was degraded Titration experiments performed in coordination with UV cross-linking studies demonstrated that the amount of poly(A) competitor RN A required to activate the S I 00 extract precisely corresponded with the ability ot the competitor to inhibit binding of proteins to the poly(A) tail of the substrate RNA (data not shown) Furthermore, the nucleolytic activities activated by the addition of cold poly(A) RNA as competitor to the S 100 extracts were still observable at concentrations of poly(A) >500 ng. These data suggest that the activated nuclease( s) is highly refractory to competition by poly(A ). The progressive shortening of the Gem-A60 RNA substrate observed upon incubation in S I 00 extract supplemented with poly(A) competitor RNA was determined to be due to a 3 ' -to-5 " . poly(A) tail-specific exonuclease based on the following observations: First. RNA substrates 32 P-labeled exclusively at their 5 " cap structures were progressively shortened in the system in a similar fashion as uniformly labeled transcripts (compare Figs. 1 A and I B). These data suggest that the shortening of the input RNA occurred in a 3 * -to-5 " direction. This conclusion was confirmed by separately analyzing the 5 " and 3 ' portions of RNA products from the in vitro system by RNAsc H digestion prior to gel electrophoresis. As shown in Fig. I C, the 3 " portion of the substrate RNA ( which consists primarily of the 60 base poly(A) tail) was clearly being degraded before any turnover of the 5 " portion of the transcript was detected. After 9 minutes of incubation. 72% of the 3 ' fragment containing the poly(A) tail is degraded, while only 19% of the 5 ' fragment has been turned over. Finally, in order to ascertain whether this 3 ' -to-5 " exonuclease activity was indeed a poly(A)-specific deadenylase. w e added 1 5 bases of non-adenylate sequence onto the 3 ' end of the Gem-A60 RNA (Gem-A60- 1 5). /As seen in Fig. 1 D. while the Gem-A60 transcript (which contains a 3 ' poly(A) tail) is an excellent substrate for the 3 ' exonuclease activity, the Gem-A60-15 RNA. which has its poly(A) tract internalized 15 bases, was not. From these data it has been concluded that the addition of poly(A) competitor RNA to an S I 00 extract activates a deadenylase which is active on exogenous. poly(A)+ substrate RNAs. The in vitro sy stem reproduces several aspects of mRNA stability observed in vivo. The surprising observation that the deadenylase itself is not apparently inhibited by cold poly(A) suggests that the native enzvme mav not have high affinity tor its substrate The deadenylase activity mav contain additional RNA binding activ ities that anchoi it to mRNAs, perhaps as part of a multi-component complex 11 RNA turnovei in the m vitro svstem is regulated bv AU-nch instability elements It was determined whether the RNA turnov er activities exhibited by the S I 00 extract system could be influenced oi modulated by sequences in the body of the transcript in a specific manner The relative stability of small polyadenylated RNAs containing either a 54 base polylinker sequence (Gem-A60), a 34 base AU-πch element (ARE) from TNF-α mRNA (ARE-A60) or a 72 base ARE from the c-tos mRNA ( I os-A60) was determined in the in vitro stability system \s shown in igs 2A and 2B. the turnover of both of the ARE-conta ing RNAs was di amaticallv increased compared to the Gem-A60 control transcript To directly assess whether regulation by AREs was occurring in a sequence-specific fashion, the TNF-α-ARE was extensively mutated as described in Materials and Methods Similar mutations in AU-nch instability elements were shown previously to greatly increase mRNA half-life in vivo ( yer et al , 1997) As seen in Fig 2C, mutations in the ARE l educed the l ate and extent of deadenv lation /degradation over 3-fold in the in vitro system Thus. RNA turnover in the in viti o svstem can be regulated or modulated by AU-nch instability elements in a sequence-specific fashion All of the RNA substrates we have examined above contain a body of approximately 50-70 bases attached to a poly (A) tail It was then determined whether regulated turnover using larger polvadenvlated RNA substrates could be detected in the svstem of the invention As shown in Fig 2D a polv adenvlated 250 base RNA deri ed fiom the 3 ' UTR of the SV40 late mRNA (SV-A60) was deadenvlated but inefficiently degraded in the in vitro system Adding the TNF-α-ARE to the 3 portion of this RNA (SVARE-A60) resulted in an approximate 3 5 fold increase in the rate of turnover Finally a nearly full length (-950 base) version of the human GM-CSF mRNA was pi epared as wel l as one in which the ARE was deleted (GM-CSF(-ARE)) Th 3 ends of these transcripts wei e polvadenylated using veast poly(A) polymerase (Martin and Keller 1998) Gel purified RNAs were incubated in the in vitro stability system and ahquots were removed at the times indicated As seen in Fig 2E, the version of the GM-CST mRNA that contains an ARE was approximately 2 5 fold less stable than GM-CSF(-ARE) in the in vitro system As seen above with other transcripts, the GM-CSF transcripts were also deadenylated in the system Deadenylation was not observable in Fig 2E due to the lack of resolution of the gel svstem employed, but can be observed using foπnaldehvde-agarose gels (data not shown) in Degradation but not deadeny lation requires ATP Transcripts with 60 adcnvlates at the 3 end were obsei v ed to undergo both deadenylation and turnover in the in \ m o system This is consistent with in vivo observations that suggest the poly(A) tail is shortened to about 30-65 bases befoi e mRNA turnover is observed (Xu et al . 1997) Since degiadation appeared to begin before the input transcript was completely deadenylated (eg Fig 2) it was difficult to quantitatively assess the effects of AU-nch elements on relative deadenvlation rates In order to trv uncoupling these processes and accurately evaluate the effect of AREs on deadenvlation l ates in the in viti o svstem, we surveyed the cofactor requirements that might be unique to either deadenylation or turnover Both processes were inhibited by the addition of EDTA (data not shown), suggesting a role for divalent cations Cm louslv deadenylation could occur without the addition of ATP/phosphocreatine to the system (Fig 3A) Degradation, on the other hand, required ATP/phosphocreatine as indicated bv the accumulation of deadenylated intermediates in its absence (Fig 3A lanes -ATP) By omitting ATP from the reaction, therefore we were able to evaluate relative deadenylation rates in the presence oi absence of an AU-nch instability element RNAs with phy siological length polv(A) tails ( 1 50-200 bases) which lack (SV-A 150-200) oi contain (SVARE-A 1 50-200) an ARE were incubated in the in vitro svstem and abquots wei e analvzed at the times indicated As seen in Fig 3 B, RNA substrates containing an ARE ere deadenv lated at an approximately two fold faster rate than RNAs that do not contain the instability element In summary an in vin o mRNA stability sv stem has been discovered that acts on exogenous substrates and faithfully l eproduces all of the known i ivo aspects of turnovei RNAs are first deadenvlated pπoi to degradation of the bodv of the ti anscnpt Degradation of the body of the mRNA then occurs in an apparently highly processive fashion with no discernible intermediates Deadenv lation and decay rates are increased several fold by the inclusion of an AU-nch instability element ARE regulation of RNA stability is sequence-specific and highly reproducible as all three of the AREs we have tested in the in vitro system function in a similar fashion This system should provide a valuable means to elucidate mechanistic aspects of regulated and general mRNA turnover pathways iv The role of ARE binding proteins in the in t o svstem The in vitro system described here allows evaluation ot the role of ARE-binding proteins in the process of RNA deadenylation/degradation Several proteins were found to be associated with ARE-containing RNAs in our extracts As seen in Fig 4A a protein of ~30 kDa and a group of ~40 kDa proteins were specifical ly UV cross-l inked to the short ARE-A60 transcript A species ot approximately 70 kDa was also detected when this ARE was inserted into a larger transcript (SVARE-A60. see F ig 5B) It is possible that this 70 kDa protein was not detected on the ARE-A60 RNA because of the relatively small size of the transcript Efforts to determine the identity of these cross linked species using available antibodies to known ARE-binding proteins revealed the pi esence ot an ELAV protein As shown in Fig 4B, lmmunoprecipitation assavs identified the 30 kDa protein as HuR (a k a HuA). a member of the ELAV protein family that is ubiquitously expressed in all tissues (Good, 1995, Ma et al , 1996 Myer et al , 1997) Antisera against another RNA-binding protein of approximately 30 kDa hnRNP A l failed to detect anv cross linked protein in our system (Fig 4B) Two additional antisera were tested in order to identify the 40 kDa band Antibodies to hnRNP C protein failed to detect anv cross linked protein while antisera to AUF- 1 (a k a hnRNP D)(Brew er 1991 ) did precipitate a small amount ot cross linked 40 kDa protein (data not shown ) However this cross linked product was not competed by increasing amounts of a 34 base synthetic \RE competitor RNA (data not shown) The significance of this low level ot non-specific AUF- 1 cross linking in the system is unciear It was concluded that the 30 kDa species that specifically ci oss links to the ARE element is HuR. a protein that has been previously suggested to plav a role in ARE-mediated mRNA decay (Vakaloloupou et al, 1991 , Antic and Keene. 1 97 Mver et al . 1997) Next, it was detei mined whethei the interaction ot the u oss linked ARE binding proteins with the element was l equired to mediate instability Sy nthetic πbonucieotides containing either a 34 base TNF-α ARE oi randomly chosen. non-ARE sequences were used Synthetic competitor RNAs were added in increasing amounts to the in vitro stability system and their effect on RNA turnover was assessed As seen in Fig 5 A. the ARE competitor RNA completely inhibited deadenylation and degi adation at 40 pm. while the non-specific RNA had no effect at similai concentrations The ARE competitor RNA had a similar effect on the deadenvlation/degradation of RNAs whethei or not they contained an ARE Thus, factors capable of interacting w ith AREs are important for deadenvlation. and may be a part of a multi-protein deadenylase/degradation complex The ability of the synthetic ARE competitor RNA to block deadenylation was compared with the ability ot the RNA to compete for interaction of ARE-binding proteins with the substrate transcript EDTA was added to cross-linking assays to inhibit RNA turnover and to evaluate the effect ot various levels of competitor on u oss-linkmg/label ti ansfer efficiency As shown in Fig 5B. all Λ RE-binding proteins ( including HuR protein that could be immunoprecipitated using specific antisera prior to gel electrophoresis as shown in panel C) were specifically competed from the SV-ARE-A60 RNA substrates upon addition of 5 pm ot the synthetic RNA competitor As shown in Fig 5 A, however, 5 pm of synthetic ARE competitor RNA failed to have an appreciable effect on the rate of RNA deadenylation/degradation in the system Hence, none of the ARE-binding proteins that could be detected by ci oss-linking appear to be required tor deadenylation/degradation in the m vitro system v FLAV pi otems prevent degradation of deadenylated transcripts in the in vitro svstem Since the ARE binding proteins we detected bv cross-linking do not appear to be required for deadenylation/degradation thev may plav a l ole in ti anscnpt stability Consistent with this model, recent in i ivo data suggest that overexpression of Hel-N 1 and HuR proteins can stabilize ARE-containmg transcripts (Jain et al . 1997 1 an and Steitz. 1998, Peng et al , 1998) A mouse recombinant HuR protein as well as other members of the ELAV family (Hel-N 1 and Hel-N2 [a k a HuB]) were pi oduced as GST fusion proteins and added these to the in vitro stability system at a 10 1 molai ratio to substrate RNA Similar data were obtained using any of the thiee l ecombinant ELAV family proteins, and only data with rHel-N l is shown As seen in Fig 6A. i Hel-N l protein failed to affect deadenylation of the SVARE-A60 RNA substrate in the in vitro system, but stabilized a deadenylated intermediate GST alone or another GST-fusion protein that binds RNA (hnRNP H') had no effect on transcript stability in the in vitro system (Fig 6B) As a result, it was concluded that the ELAV family ot RNA binding proteins function to protect deadenylated transcripts from the degradation enzvmes Next, it was tested whether the RNA substiate must contain an ARE in order for rELAV proteins to stabilize a deadenylated intermediate in the m vitro system ARE-A60 RNA, or an unrelated but similai ly sized and polyadenylated transcript, CX-A60. were incubated in the in vitro system in the presence oi absence of rELAV proteins As seen in Fig 6C, rHelN l (or other rELAV proteins [data not shown]) stabilized the deadenylated intermediate only from RNAs that contain an ARE binding site Thus the stabilization of deadenylated intermediates by ELAV proteins requires an ARE Furthermore. ELAV proteins can stabilize a deadenylated intermediate whether the ARE is located at the 3 ', 5 * or central positions of the 250 base SVARE-A60 RNA These data indicate that the ARE-ELAV protein complex probably is not simply preventing turnover through steric blocking of an end of the transcript, thereby preventing exonuclease access Set forth herein is a nov el and useful in viti o RNA stability system that faithfully reproduces many known aspects of in vivo mRNA turnover in mammalian cells Exogenous RNA substrates are deadenvlated before degradation of the RNA body occurs in an apparently highly processive fashion without detectable intermediates Furthermore, the rates of RNA deadenylation and degi adation are regulated by AU-nch elements in the system in a sequence-specific manner The svstem ot the invention has been successfully used to determine a le tor the LLAV family ot ARE binding proteins in the stability of deadenylated transcripts by specifically blocking the degradation step These data illustrate the value of the system to address the mechanism of legulated mRNA turnover. The in vitro system described in this report has several key technical advantages that significantly increase its utility First, the system is highly reproducible and uses standard S 100 cytoplasmic extiacts from Hela spinnei cells In fact, nine independent preparations of S 100 extract that all function in the assay m a similar fashion have been tested The only difference among extiacts appears to be in the kinetics of turnover (e g compare the slight differences in the pattern of turnover of Gem-A60 RNA in Fig 1 A with the pattern observed in Fig. I D) Second, the extracts exhibit minimal background degradation of RNA due to non-specific nucleases This lack of noise in the system significantly contributes to its reproducibibty Another key element of the system is that is uses exogenous polyadenylated RNAs as substrates This property affords variety in RNA substrate preparation and sequence manipulation Fourth, the system exhibits sequence-specific regulation by AU-nch elements in the absence of translation In total, these technical advantages make the system a valuable reagent to identify components involved in mRNA turnover and address the mechanism of regulated mRNA stability The addition of poly(A) competitor RNA was required to activate SI 00 extracts to efficiently deadenylate and degrade RNAs in a regulated manner Titration of cold poly(A) demonstrated that the extracts became activated for deadenylation/degradation when sufficient competitor was added to substantially leduce cioss linking of a 70 kDa poly(A) binding piotem to the poly(A) tail ot the radiolabeled substrate RNA (data not shown) Surprisingly, the deadenylation in the extracts remain active even in the presence of >500 ng of poly(A) Commercial poly(A) preparations prepared with polynucleotide phosphoryiase, therefore, do not appear to be able to interact with and sequester the deadenylase enzyme These data suggest that the deadenylase activity is eithei in extraordinary concentrations in the extracts or may not have a strong affinity for its substrate In conjunction with this, it has been observed that an increase in deadenylation rate ot ARE containing RNAs (Figs. 2 and 3). as well as the ability of the ARE competitor RNA to inhibit deadenylation of non-ARE containing substrates These data suggest that ARE-binding proteins may be associated with the deadenvlase activity Moreover, HuR protein, a ubiquitously expi essed member of the ELAV family of RNA binding proteins (Good. 1995. Ma et al , 1996. Myer et al . 1997. Antic and Keene. 1997), has been identified as one of the ma|or ARE binding factors in the system of the invention. Also, the system of the invention has been successfully used to detect weak binding to AUF- 1 (hnRNP D), a piotein previously speculated to be involved in regulated mRNA decay in vitro (DeMaπa and Brewer. 1996) AUT- 1. therefoi e. does not appear to play a significant role in transcript instability in our system ELAV proteins are not required for deadenylation/degradation, but rather play a le in the stability of deadenylated RNAs that contain an ARE (Fig 6) These data suggest that in addition to its effect on deadenylation rates (Chen et al . 1995. Xu et al , 1997), the ARE influences the efficiency of turnover of the body of the mRNA /;; vivo observations (Chen et al.. 1995. Xu et al , 1997. Peng et al.. 1998) also support the conclusion that ARE influences mRNA degradation rates ELAV proteins, therefoie. appear to regulate mRNA stability in vitro, an observation consistent with in vivo tiansfection studies The ELAV family comprises four members, three of which are expi essed in a tissue or developmental specific manner (reviewed in Antic and Keene, 1997) Tissue-specific ELAV proteins are also localized primarily to the cytoplasm, while the ubiquitous HuR protein is predominantly nuclear and can redistribute to the cytoplasm (Atasoy et al . 1998, Peng et al , 1998, Fan and Steitz, 1998) It has been suggested that differentially expressed ELAV proteins play a role in regulating the stability of both nuclear and cytoplasmic RNA, theieby fine tuning gene expression in specific developmental states (Gao and Keene. 1996. Antic and Keene. 1998) The competition data shown in Fig 5 cleai ly demonstrate that factors associated with the ARE are required for deadenylation/degradation of substrate RNAs. Based on the kinetics of competition, these factois must either be much more abundant than the cross-linkable ARE binding proteins like HuR. or interact with the ARE with a much lower affinity We favor the latter model, and suggest that these factors are part of a multi-component complex that includes the deadenylase and degradation enzymes Thiough multiple cooperative interactions, these weak ARE binding components may allow efficient assembly of the deadenylase/degradation complex on ARE containing tr anscripts while still allowing the complex to assemble, albeit less effectively on non-ARE containing RNAs The RNA binding components ot this proposed complex also mav have affinity for other non-ARE instability elements (e g Peng et al 1996) The observation that endogenous FIuR protein in S I 00 extracts set forth herein can be cross-linked to ARE-containing RNA substiates (Fig 3 ) makes it surprising that an ARE can function as a destabbzing element in the in i o assay Since HuR protein is predominantly nuclear however onlv low levels of the protein are likely to be present in our cytoplasmic extracts This low lev el of HuR protein is probablv unable to efficiently compete with destabbzing factoi s foi binding to the ARE In fact, sequestration of the HuR protein by the addition of low levels ot synthetic ARE competitor RNA does lead to an increased rate ot turnover of ARE-containing RNAs in the in i itro system As shown in Fig 5 A. the amount of SVARE-A60 RNA l emainmg after 30 mm in the svstem in the absence of competitor RNA (lane 0) is approximately 20% greater than when the assay is done in the presence of 5 pm of ARE competitor RNA (lane 5 pm) T he removal or sequestration of HuR protein in S I 00 extracts, therefoi e may be necessary in oider to observe regulated deadenylation and degradation in some instances Materials and Methods Transcription templates and RNAs RNAs were produced bv in viti o transcription using SP6 polvmeiase (Melton et al . 1984) in the presence of 7m GpppG cap analog and radiolabeled UTP or A TP as indicated All transcripts were gel pin ified pi ioi to use I or RNAs labeled exclusively at the 5 cap, transcription reactions wei e pei formed in the absence ot cap analog and radioactive nucleotides Capping w as then performed using guanv Iti ansferase (BRL) and radiolabled GTP according to the manufacturer s recommendations The sequence of short RNAs used as substrates in the in t o svstem is shown in Table 1 Transcription templates were derived as follows ( Please note that all synthetic oligonucleotides used as transcription templates shown below contain a 24 base SP6 promoter fragment at their 5 ends) Gem-AO RNA was pioduced from Hind III cut pGem4 (Promega) Geιn-A60- 1 5 RNA was produced from the PCR product used to produce Gem-A60 RNA (see belo ) w ithout removing the primer binding site with Ssp I Templates for ARE-AO RNA wei e generated by hybridizing the sv nthetic oligonucleotide 5 -ATTTAGGTGACACTATAGAATACAC ATTATTTATTATTTATTTATTATTTATTTA TTTA-3 ' (SEQ ID NO 1 ) and its appropriate complement Templates for MT-ARE-AO RNA were generated bv hybridizing the synthetic oligonucleotide 5 " -ATTTAGGTGACACTATAGAATACAC G TTAGTATTCATTTGTTTACTATTGATTTC TTTA-3 ' (SEQ ID NO 2) and its appropriate complement Templates for Fos-AO RNA were generated by hybridizing the synthetic oligonucleotide 5 ' -ATTTAGGTGACΛCTATAGAATACACAAATTTTATTGTGTTTTTAATTTATTTATT AAGATGGATTCTC-3 ' (SEQ ID NO 3) and its appropriate complement The template for SV-AO RNA was Hind III cut pSVL-Gem (Wilusz et al . 1988) Templates for SVARE-AO RNA were generated by inserting the TNF-α ARE containing oligonucleotide 5 -ATTATTTATTATTTATTTATTATTTATTATTTΛ ( SEQ I D NO 4) and its appropriate complement between the Pstl and Hind II I sites of pSVI -Gem ( located near the 3 " end of the RNA) SVARE-AO RNA was transcribed i i om Hind II I linearized DNA The template for GM-CSF (+ARE) RN Λ was EcoRI cut pGM-CSF (Shaw and Kamen. 1986) The template for GM-CSF (-ARE) RNA was Ncol cut pGM-CSF Templates for CX-AO RNA were generated by hybridizing the synthetic oligonucleotide 5 " -ATTTAGGTGACACTATAGAATACACCCCAACGGGCCCTCCCTCCCCTCCTTGCA CCATCATCGCATCACG (SEQ ID NO 5) and its appropriate complement Synthetic RNAs used in competition studies were made by the NJMS Molecular Core Facility and contained the following sequences ARE 5 AUUAUUUAUUAUUUAUUUAUUAUUUAUUUAUUUA (SEQ ID NO 6) Non-specific competitor S '-GUCACGUGUCACC (SEQ ID NO 7) Addition of Polv(A) tails to transcripts A template for a 60 base poly(A) tail was added to DNA templates using a Iigation/PCR protocol have recently been described (Ford et al , 1997) Briefly, all of the templates described above contain a Hind III site that is used to generate the 3 * end of the RNA The synthetic oligonucleotide 5 " -AGCTA fl0 TATTGAGGTGCTCGAGGT (SEQ ID NO 8) and its appropriate complement were generated, hybridized, and ligated to Hind III cut DNA templates Ligation pi oducts ei e amplified using an SP6 promoter primer (5 " -CATACGATTTAGGTGACACTATAG (SEQ ID NO 9)) and a primer specific for the 3 ' -33- end of the ligated oligonucleotide (5 ' -ACCTCGAGCACCTC (SEQ ID NO: 10)). Amplified products were purified on Centricon 1 00 columns, cut with Sspl, and used as templates for SP6 polymerase generate RNAs carrying the 'A60' designation. Poly(A) polymerase ( Amersham ) was used to add 150-200 base poly(A) tails onto transcripts. RNAs were incubated with enzyme according to the manufacturers recommendations on ice for 5-8 min. Following the reaction. RNAs were extracted with phenol-chloroform, ethanol precipitated, and purified on 5% acrylamide gels containing 7M urea to obtain RNAs with the appropriate amount of poly(A) at the 3' end. S I 00 extract production Cytoplasmic extracts were prepared from Hela spinner cells grown in JMEM supplemented with 1 0% horse serum as described by Dignam et al ( 1 83) with the following two modifications. First, following centrifugation at 100.000 x g for 1 hr. the supernatant was adjusted to 10% glycerol prior to dialysis. Second, dialysis times were shortened to 30 min. Extracts were stored at -80"C. In vitro RNA deadenylation/degradation svstem Typically, approximately 200.000 cpm (~50 fm) of gel purified RNA is used per reaction. In comparative studies, equal molar amounts of transcripts were used. A typical 14.25 μl reaction mixture contains 3.25 μl of 10% polyvinyl alcohol, 1 μl of a 12.5 mM ATP/ 250 mM phosphocreatine mixture. 1 μl of 500 ng/ul poIy(A) (Pharmacia), 1 μl of RNA and 8 μl of dialyzed extract. Reactions were incubated at 30° C for the times indicated and stopped by the addition of 400 μl of stop buffer (400 mM NaCl. 25 mM Tris-Cl, pH 7.6. 0.1 % SDS). Reaction mixtures were phenol extracted, ethanol precipitated and analyzed on a 5% acrylamide gel containing 7M urea. All quantitation was performed using a Molecular Dynamics Phosphorimager. Recombinant ELAV proteins ( HuR, Hel-N 1 and Hel-N2) were made as GST-fusion proteins in E. coli and purified using glutathione-sepharose affinity chromatography according to the manufacturer ' s recommendations (Levine et al. 1993). RNase H digestion ARE-A60 RNA ladiolabeled at A l esidues was incubated in the in vitro stability system for the times indicated RNA products were phenol extracted and concentrated by ethanol precipitation The sample was resuspended in a final volume of 30 μl containing 20 mM Tris-Cl. pH 8 0. 100 m M NaCl. 10 mM MgCL, 1 mM DTT 100 picomoles of the antisense oligonucleotide 5 ' -AGTTAAATAAAT (SEQ ID NO 1 I ), and 1 unit of RNase H Reactions were incubated at 37°C for 30 min and pioducts were analyzed on a 5% acrylamide gel containing 7 M urea UV Cross linking and Immunoprecipitations UV cross linking/label transfer experiments were performed as described previously using a Sylvania G 15T8 germicidal light (Wilusz and Shenk, 1988) Cross linking experiments were done in the presence of 25 mM EDTA to inhibit RNA turnover to allow for accurate comparisons betw een samples Following digestion with RNAses A. Tl and T2. ci oss linked proteins were analvzed on 10% acrv lamide gels containing SDS For lmmunoprecipitation analvsis follow ing UV cross linking and RNAse treatment. 300 μl of RIPA buffer (0 15M NaCl, 1 % NP-40 0 5% deoxycholate. 0 1 % SDS and 50 mM Tπs-Cl. pH 7 6) was added to samples Following a brief centi ifugation in a microfuge, precleared samples were incubated on ice ith antibodies for 1 hi Antigen-antibody complexes were collected using formalin fixed washed protein-A positive S aureus cells, washed five times using RIPA buffer, and analyzed on a 10% acrylamide gel containing SDS Antibodies specific for GRSF (Qian and Wilusz. 1994) and hnRNP A l (Wilusz and Shenk, 1990) have been described previously The preparation and characterization of rabbit polyclonal antibodies specific foi HuR will be described elsewhere (Atasoy et al . 1998) Aghib, D F . Bishop, I M , Ottolenghi. S Guerrasio. A Serra, A . and Saglio, G 1990 A 3 ' ti uncation of mvc caused by chromosomal translocation in a human T-cell leukemia increases mRNA stability Oncogene 5: 707-71 1 Anderson. J S J . and Parker. R 1998 The 3 to 5 ' degi adation of yeast mRNAs is a general mechanism for mRNA turnover that requires the SK12 DEVH box protein and 3 ' to 5 " exonuclease of the exosome complex EMBO J 17: 1497- 1506 -33- Antic. D . and Keene 1 D 1997 Embryonic lethal abnormal visual RNA-binding proteins involved in growth differentiation and posttranscriptional gene expression Am J Hum Genet 61 : 273-278 Antic, D , and Keene. I D 1998 Messengei i ibonucleoprotein complexes containing human ELAV proteins liitei actions w ith cytoskeleton and translational apparatus J Cell Sci 111 : 1 83- 197 Atasoy, U , Watson. J . Patel. D , and Keene. J D 1998 Ubiquitously-expressed ELAV RNA binding protein. 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J L 1997 Mechanism and l egulation of mRNA polyadenylation Genes Dev 11: 2755-2766 DeMaπa, C T , and Bi ewei . G 1996 AUT 1 binding affinity to A+U-πch elements correlates with rapid mRNA degiadation I Biol Chem 271 : 12179- 12184 Dignam. J D , Lebovitz R M . and Roedei . R G 1983 Accurate transcription initiation by RNA polymerase II in a soluble extract from isolated mammalian nuclei Nucl Acids Res 11: 1475- 1489 Fan. X C , Myer. V E and Steitz. J A 1997 AU-nch elements target small nuclear RNAs as well as mRNAs foi l apid degradation Genes Dev 11 : 2557-2568 ran. X C , and Steitz, J A 1998 Overexpiession of HuR. a nuclear-cytoplasmic shuttling protein, increases the in vivo stability of ARE-containing mRNAs EMBO J 17: 3448-3460 Ford, L P , Bagga, P S . and Wilusz. J 1997 The poly(A) tail inhibits the assembly of a 3 " -to-5 " exonuclease m an in v lti o RNA stability system Mol Cell Biol 17: 398-406 Furuichi.Y . LaFiandra A . and Shatkin, A I 1977 5 ' -terminal structure and mRNA stability Nature 266: 235-239 Gao. F B . and Keene J D 1996 Hel-N 1 /Hel-N2 proteins are bound to poly(A)+ mRNA in granular RNP structui cs and are implicated in neuronal differentiation J Cell Sci 109: 579-589 Good. P J 1995 A conserved family of elav-like genes in vertebrates Proc Natl Acad Sci USA 92: 4557-4561 Hamilton, B J . Nagy L Maker. J S . Ai nck. B A . and Rigby, W F C 1993 Association of heterogeneous nuclear i ibonucleoprotein A l and C proteins with reiterated AUUUA sequences J Biol Chem 268: 8881 -8887 Holcik. M . and Liebhaber. S A 1997 Foui highly stable eukarvotic mRNAs assemble 3 ' untranslated region RNA-prote complexes sharing cis and trans components Proc Natl Acad Sci USA 94: 2410-2414 Iain, R G . Andrews, L G , McGowan, K M Pekala. P H . and Keene, J D 1997 Ectopic expression of Hel-N 1 an RNA binding protein, increases glucose transporter (GLUT 1 ) expression in 3T3-L1 adipocytes Mol Cell Biol 17: 954-962 Jacobson, A . and Peltz S W 1996 Interrelationships between the pathwavs of mRNA decay and translation in eukaryotic cells Annu Rev B iochem 65: 693-740 Katz, D A , Theodorakis N G . Cleveland, D W . Lindsten, T , and Thompson. C B 1994 AU-A, an RNA binding activity distinct from hnRNP A 1 , is selective for AUUUA repeats and shuttles between the nucleus and the cytoplasm Nucl Acids Res 22: 238-246 Korner, C G , and Wahle E 1997 Poly( A) tail shortening by a mammalian poly(A)-specιfic 3 -exoi ibonuclease J Biol Chem 272: 10448- 10456 Koushika. S P . Lisbon M J . and White, K 1996 ELAV. a Drosophila neuron-specific protein, mediates the generation of an alternatively spliced neural protein isoform Curr -38- Lagnado. C A . Brown C Y . and Goodall G J 1994 AUUUA is not sufficient to promote poly(A) shortening and degradation ot a mRNA the functional sequence within AU-nch elements mav be U UAl UUA(U/A)( U/A ) Mol Cell Biol 14: 7984-7995 Levine. T D , Gao F king. P H . Andrew s L G . and Keene. J D 1993 Hel-N l an autoimmune RNA-bmding protein w ith specificity for 1 uπdylate-rich untranslated regions of growth factor mRNAs Mol Cell Biol 13: 3494-3504 Levy. N S Chung, S Turneaux. FI and Levy. A P 1998 Hypoxic stabilization of vascular endothehal gi owth factor mRNA by the RNA-binding pi otein HuR J Biol Chem 273: 6417-6423 Ma. W -J . Cheng S Wright. Λ . Campbel l. C . and Fui neaux. I I 1996 Cloning and characterization of HuR a ubiquitously expi essed Elav-l ike protein J Biol Chem 271 : 8144-8151 Ma. W - I . C|ung S and Furneaux H 1997 The elav -like proteins bind to AU-nch elements and to the polv(A) tail of mRNA Nucl Acids Res 25: 3564-3569 Maker. J S 1989 Identification ot an AUUUA-specific messenger RNA binding protein Science 246: 664-666 Martin. G . and Kellei W 1998 Tailing and 3 -end labeling ot RNA with veast poiy(A) polymerase and various nucleotides RNA 4: 226-230 Maquat. L E 1995 hen cells stop making sense effects of nonsense codons on RNA metabolism in vertebrate ceils RNA 1 : 453-465 Melton. D A , Kπeg. P A , Rebagbati. M R Ma atis. I . Zinn. K . and Green. M R 1984 Efficient in vitro svnthesis of biologically active RNA and RNA hybridization probes from plasmids containing a bactenophage SP6 pi omoter N ucl Acids Res 12: 7035-7056 Muhlrad. D . Deckel C I . and Parker. R 1 94 Deadenv lation ot the unstable mRNA encoded bv the veast M FA2 gene leads to decappmg followed bv 5 to 3 digestion of the transcript Genes Dev 8: 855-866 Myer V E . Fan. X C and Steitz. J A 199 "? Identification of HuR as a protein implicated in AUUUA-mediated m RNA decay EMBO I 16: 2130-2139 Nakagawa, J , Waldnei H Mever-Monai d S Hofsteenge. J . Jeno. P . and Moronoi. C 1995 AUH. a nov el gene encoding an AU-specific RNA binding protein with intrinsic enoyl-CoA hydralase activity Proc Natl Acad Sci USA 92: 2051 -2055 Peng. S S -Y , Chen. C -Y A . and Shyu A -B 1996 Functional characterization of a non-AUUUA AU-nch element from the c-μin proto-oncogene mRNA evidence for a novel class of AU-nch elements Mol Cell Biol 16: 1490- 1499 Peng, S -Y Chen C ) A Xu N . and Shvu. A -B 1998 RNA stabilization by the AU-nch element binding protein. HuR. an LL AV protein LMBO J 17: 3461 -3470 Presutti. C . Villa, T , Hall. D Pertica, C and Bozzom I 1995 Identification of the cis-elements mediating the autogenous contiol of nbosomal protein L2 mRNA stability in yeast EMBO J 14: 4022-4030 Qian. Z . and Wilusz i 1994 GRSF- 1 a polv(A)+ m RNA binding protein which interacts with a conserved G-i ich element Nucl Acids Res 22: 2334-2343 Ross, J 1995 mRNA stability in mammalian cells M icrobiol Rev 59: 16-95 Robinow. S . and White. K 1988 The locus elav of Di osophila melanogaster is expressed in neurons at all developmental stages Dev Biol 126: 294-303 Scluavi S C Belasco I G and Gi eenbei g L 1992 Regulation ot proto-oncogene mRNA stability Biochun Biophv s Acta 1 114: 95- 106 Shaw. G . and Kamen R 1986 A conserv ed AU 1 ich sequence from the 3 untranslated region of GM-CST in R A mediates selectiv e mRNA degradation Cell 46: 659-667 Shyu. A -B Belasco I G . and Greenberg L 1989 The c-tos transcript is targeted tor rapid decav by two distinct mRNA degradation pathway s Genes Dev 3: 60-72 Stefanovic. B . Hellerbi and, C Holcik. M Bnendl. M Liebhaber S A , and Brenner, D A 1997 Posttranscriptional regulation of collagen a I (I) m RNA in hepatic stellate cells Mol Tarun, S Z . and Sachs A B 1997 Association ot the v east polv(A) tail binding protein with translation initiation factoi eιf-4G EMBO I 15: 7 1 68-71 77 Vakaiopouiou. E Schaack. J and Shenk T 1991 A 32-kιlodalton protein binds to AU-nch domains in the 3 " untranslated regions of rapidly degraded mRNAs Mol Cell Biol 11: 3355-3364 Weng. Y . Ruiz-Echev ai na. M J Zhang, S Cm, Y Czaplinski. K Dinman. J D , and Peltz, S W 1 997 Chaiactei ization ot the nonsense-mediated mRNA decay pathway and its effect on modulating tr anslation tei mination and programmed frameshifting In "mRNA Metabolism and Post- 1 1 anscπptional Gene Regulation 1 B Harfoi d. D R Morris, eds . Wilev-Liss. Inc . New ork. pp 241 -263 Wilson. T . and Tieisman. R 1988 Removal of poly (A) tail and consequent degradation of c-fos mRNA facilitated by 3 AU-nch sequence Natui e 366: 396-399 Wilusz. J . and Shenk T 1988 A 64 kDa nuclear protein binds to RNA segments that include the AAUAAA poly adenvlation motif Cell 52: 221-228 Wilusz. J Feig, D I and Shenk T 1988 The C proteins of heterogeneous nuclear nbonucleoprotein complexes interact with RNA sequences downstream of polyadenylation cleavage sites Mol l l Biol 8: 4477-4483 Wilusz. J , and Shenk T 1990 A undvlate tract mediates efficient heterogeneous nuclear πbonucleoprotein C pi otein-RNA cross-linking and functionally substitutes for the downstream element of the polyadenylation signal Mol Cell Biol 10: 6397-6407 Wormington. M . Seai toss. A M . and Hurnev. C A 1996 Overexpression ot poly(A) binding protein prevents maturation-specific deadenvlation and translational inactivation in Xenopus oocytes EMBO J 15: 900-909 Xu, N , Chen. C -Y A and Shvu, A -B 1997 Modulation of the fate of cytoplasmic mRNA by AU-nch elements key sequence features controlling mRNA deadenylation and decay Mol Cell Biol 17: 461 1 -4621 Zubiaga, A M , Belasco J G . and Greenbei g. M E 1995 The nonamer UU AUUUAUU is the key AU-nch sequence motif that mediates mRNA degradation Mol Cell Biol 15: 2219-2230 The piesent invention is not to be limited in scope by the specific embodiments describe herein Indeed, various modifications of the invention in addition to those described herein will become apparent to those skilled in the art from the foregoing description and the accompanying figures Such modifications ai e intended to fall within the scope of the appended claims It is further to be undei stood that all base sizes or amino acid sizes, and all molecular weight or molecular mass values, given for nucleic acids or polv peptides are approximate and are provided for description Various publications ai e cited herein the disclosures of which are incorporated by reference in their entireties

Claims: WHAT IS CLAIMED IS 1 An in vitro system capable of recapitulating regulated RNA turnover of an exogenously added preselected target RNA sequence comprising a cell extract and said target RNA sequence 2 The system of claim 1 wherein said regulated RNA turnover is selected from the group consisting of AU-i ich element regulated RNA turnover and C-πch element regulated turnover 3 The system of claim 1 wherein said cell extract is isolated fi om lysed eukaryotic cells or tissues 4 The system of claim 3 wherein said cell extract is obtained from a cell line selected from the group consisting of HeLa cells and a T cell line 5 The system of claim 1 wherein said cell extract is prepared from cells comprising foreign nucleic acid 6 The system of claim 1 wherein said cell extract is pi epared from cells which are infected, stably transfected, oi transiently transfected 7 The system of claim 1 wherein said cell extract is partially purified 8 The system of claim 1 wherein said cell extract is depleted of activity of proteins that bind polyadenylate 9 The system ot claim 8 wherein said cell extract depleted of activity of proteins that bind polyadenylate is prepared by a method selected from the group consisting of (a) addition to said system of polyadenylate competitor RNA, (b) sequestration of proteins that bind polyadenylate. (c) addition ot a protemase that inactivates a pi otein that bind to polyadenylate. and (d) addition ot ΔIΛ agent that prevents the interaction between polvadenvlate and an endogenous macromolecule that binds to polvadenvlate The system of claim 9 wherein said sequestration of proteins that bind polyadenylate is achieved bv treatment of said extract with an material that depletes macromolecules that bind polvadenvlate selected from the group consisting of antibodies to proteins that bind polvadenv late polvadenvlate. and the combination thereof The system of claim 10 wherein said material is attached to a matrix The system of ciaim 1 wherein said target RNA sequence is selected from the group of synthetic RNA, naturally occurring RNA, messenger RNA. chemically modified RNA and RNA- DNA derivatives The system of claim 12 wherein said target RNA sequence comprises a 5' cap and a 3' polyadenylate sequence The system of claim 1 wherein said target RNA sequence is selected from the group consisting of unlabeled target RNA sequence, labeled target RNA sequence and the combination thereof The system of claim 14 wherein said labeled tai get RNA sequence is labeled with a moiety is selected from the group consisting of a fluorescent moiety, a visible moiety, a radioactive moietv, a ligand, and a combination of fluorescent and quenching moieties The svstem of claim 1 additionally comprising exogenously added nucleotide tnphosphate The svstem of claim 16 wherein said nucleotide tnphosphate is ATP The system ot claim 1 further comprising a reaction enhancer The system ot claim 1 8 wherein said reaction enhancer is selected from the group consisting of polvvmvl alcohol, polwmylpyrrolidone and dextran The system ot claim 19 wherein said reaction enhancer is polyvinyi alcohol A method for identifying an agent capable of modulating the stability of a target RNA sequence comprising (A) pi ovidine the system ot claim 1 , (B) introducing said agent into said sy stem, (C) determining the extent of turnover ot said target RNA sequence, and (D) identify ing an agent able to modulate the extent of said turnover as capable ot modulating the stability of said target RNA sequence The method of claim 21 wherein said system additionally comprises nucleotide tnphosphate The method of claim 22 wherein said nucleotide tnphosphate is ATP The method ot claim 21 wherein said agent is an RNA stability modifying molecule The method ol claim 2 1 wherein said target RNA sequence is selected from the group consisting of unlabeled target RNA sequence, labeled target RNA sequence. and the combination thereof The method of claim 25 wherein said labeled RNA sequence is labeled with a moiety is selected from the group consisting of a fluoi escent moiety, a visible moiety, a radioactive moiety a ligand, and a combination of fluorescent and quenching moieties The method of claim 21 wherein said monitoring the extent of turnover of said target RNA sequence comprises determining the extent of degradation of said labeled target RNA The method of claim 21 wherein said modulating the stability of a target RNA sequence increases the stability ot said target RNA sequence The method ot claim 21 wherein said modulating the stability of a target RNA sequence decreases the stability ot said RNA sequence The method ot claim 21 wherein said agent is capable of modulating the activity of a AU rich element binding protein oi a C-πch element binding protein The method of claim 30 wherein said AU I ich element binding protein is selected from the group consisting of a member of the ELAV protein family, AUF1 , tnstetrapolin. AUH. TIA. TIAR. glvceraldehyde-3-phosphate. hnRNP C. hnRNP A l . AU-A. and AU-B The method of claim 3 1 wherein said member ot the ELAV protein family is selected from the group consisting of HuR, Hel-N 1. HuC and HuD A method for identifying an agent capable of modulating the stability of a target RNA sequence in the presence of an exogenously added RNA stability modifier comprising (a) providing the system of claim 1 , (b) introducing said RNA stability modifiei into said system. (c) introducing said agent into said system (d) determining the extent of turnover of said target RNA sequence, and (e) identifying an agent able to modulate the extent of said turnover as capable of modulating the stability of said target RNA sequence in the presence of said exogenously added RNA stability modifier The method ot claim 33 wherein said system additionally comprises nucleotide tnphosphate The method of claim 34 wherein said nucleotide tnphosphate is ATP 36. The method of claim 33 wherein said target RNA sequence is selected from the group consisting of unlabeled target RNA sequence, labeled target RNA sequence. and the combination thereof. 37. The method of claim 36 wherein said labeled RNA sequence is labeled with a moiety is selected from the group consisting of a fluorescent moiety, a visible moiety, a radioactive moiety, a ligand. and a combination of fluorescent and quenching moieties. 38. The method of claim 33 wherein said determining the extent of turnover of said target RNA sequence comprises determining the extent of degradation of said labeled target RNA. 39. The method of claim 33 wherein said RNA stability modifier increases the stability of said target RNA sequence. 40. The method of claim 39 wherein said agent decreases the stability of said target RNA sequence increased by said RNA stability modifier. 41. The method of claim 33 wherein said RNA stability modifier decreases the stability of said target RNA sequence. 42. The method of claim 41 wherein said agent increases the stability of said target RNA sequence decreased by said RNA stability modifier. 43. The method of claim 33 wherein said agent is capable of modulating the activity of a AU rich element binding protein or a C-rich element binding protein. 44. The method of claim 43 wherein said AU rich element binding protein is selected from the group consisting of a member of the ELAV protein family; AUF1 ; tnstetrapolin: AUH; TIA; TIAR; glyceraldehyde-3-phosphate: hnRNP C: hnRNP Al ; AU-A; and AU-B. 45. The method of claim 44 wherein said member of the ELAV protein family is selected from the group consisting of HuR. Hel-N 1. HuC and HuD. 46. A method for identifying an agent capable of modulating the deadenylation of a target RNA sequence comprising (A) providing the system of claim 1 in the absence of a nucleotide tnphosphate; (B) introducing said agent into said system; (C) monitoring the deadenylation of said target RNA sequence in said system; and (D) identifying an agent able to modulate the extent of said deadenylation as capable of modulating the deadenylation of said target RNA sequence. 47. A method for identifying an agent capable of modulating the deadenylation and degradation of a target RNA sequence comprising (A) providing the system of claim 1 in the presence of a nucleotide tnphosphate; (B) introducing said agent into said system; (C) monitoring the deadenylation and degradation of said target RNA sequence in said system: and (D) identifying an agent able to modulate the extent of said deadenylation and degradation as capable of modulating the deadenylation and degradation of said target RNA sequence. 48. A method for identifying an agent capable of modulating cell growth or cell differentiation in a mammal comprising determining the ability of said agent to modulate the stability of a target RNA sequence involved in the modulation of cell growth or differentiation in accordance with claim 19. 49. The method of claim 48 wherein said agent capable of modulating cell growth or cell differentiation intervenes in cellular transformation. 50. The method of claim 48 wherein said agent capable of modulating cell growth or cell differentiation intervenes in immune dysregulation. 51. A method for identifying, characterizing or isolating an endogenous molecule suspected of participating in the deadenylation or degradation of RNA or regulation thereof comprising (A) providing the system of claim 1 ; (B) introducing said protein suspected of participating in the regulation of RNA turnover into said system; (C) monitoring the stability of said target RNA sequence in said system; and (D) identifying, characterizing or isolating said endogenous molecule able to modulate said deadenylation or degradation as capable of participating in the deadenylation or degradation of RNA or regulation thereof. 52. The method of ciaim 51 wherein said molecule suspected of participating in the deadenylation or degradation of RNA or regulation thereof is protein or RNA. 53. A kit for monitoring the stability of a preselected target RNA sequence under conditions capable of recapitulating regulated RNA turnover, said kit comprising: (a) cell extract depleted of activity of proteins that bind polyadenylate; (b) other reagents: and (c) directions for use of said kit. 54. The kit of claim 53 further comprising nucleotide triphosphates, a reaction enhancer, a target RNA sequence, or any combination thereof. 55. A method for identifying an agent capable of modulating the degradation a target RNA sequence in the absence of deadenylation comprising (A) providing a cell extract in the presence of a nucleotide tnphosphate; (B) introducing said agent into said cell extract; and (C) monitoring the degradation of said target RNA sequence in said extract.

Inventors: FORD LANCE P, WILUSZ JEFFREY, FORD, LANCE, P., WILUSZ, JEFFREY
Applicants: FORD LANCE P, UNIV NEW JERSEY MED, WILUSZ JEFFREY, FORD, LANCE, P., UNIVERSITY OF MEDICINE AND DENTISTRY OF NEW JERSEY, WILUSZ, JEFFREY
Application year: 1999
Main classification: C12N15
IPC codes: C12N15, C12P19, C12Q1, C40B40