ENHANCEMENT OF RIBOZYME CATALYTIC ACTIVITY BY A NEIGHBORING FACILITATOR OLIGONUCLEOTIDE

Abstract: Methods are disclosed for increasing ribozyme catalytic activity without reducing specificity, which methods comprise contacting an RNA molecule with a ribozyme and a facilitator oligonucleotide. The present invention further provides compositions comprising a ribozyme and an effective amount of a facilitator oligonucleotide. Methods are also disclosed for reducing the concentration of Mg<2+> and Mn<2+> required by a ribozyme to catalytically cleave target RNA.

Description: ENHANCEMENT OF RIBOZYME CATALYTIC ACTIVITY BY A NEIGHBORING FACILITATOR OLIGONUCLEOTIDE This application is a continuation-in-part of U.S. Patent Application Serial No. 07/830,713, filed February 4, 1992. BACKGROUND OF THE INVENTION Field of the Invention This invention relates to ribozymes that cleave RNA, and more specifically to the enhancement of ribozyme catalytic activity using a facilitator oligonucleotide complementary to an RNA sequence near or contiguous to the ribozyme. Furthermore, the invention relates to methods and compositions for treating humans and other mammals having various viral infections. Description of the Related Art Drugs might be based on RNA catalysts (ribozymes) designed to cleave viral or messenger RNA with high specificity at a rapid rate. These requirements historically have been mutually limiting. Ribozymes consist of a catalytic core having flanking sequences adjacent the core which hybridize to the substrate RNA. The simplest catalytic core is an RNA motif known as a hammerhead. Ribozyme specificity depends on the number of base pairs formed between the ribozyme flanking sequences and its RNA substrate. Increased base pairing has been shown to decrease the rate of cleavage. Goodchild and Kohli, Arch. Bioche . Biophys., 284: 386-391 (1991). Goodchild and Kohli studied the cleavage of a sequence from HIV-l RNA by various hammerhead ribozymes and determined that the rate of cleavage was dependent on the length of the flanking sequence. Shorter sequences were shown to result in weaker binding between the ribozyme and the cleavage products together with increased rate of cleavage. A ribozyme with 12 flanking sequences cleaved 10 times faster then one with 20 bases. However, to have the requisite selectivity or specifity, i.e., the ability to discriminate between all RNA molecules in a cell, a ribozyme must form a minimum of about 15 base pairs with the target substrate. This requirement for selectivity limits the rate of cleavage that may be realized. Accordingly, ribozymes having increased catalytic activity or methods of increasing ribozyme catalytic activity are needed. Further, coordination of Mg 2+ or Mn 2+ to a ribozyme at the active site is normally required for the ribozyme to catalyze sequence specific phosphodiester cleavage of an external RNA oligonucleotide substrate. See Nature, 361: 182-185 (Lehman and Joyce, 1993) . The required concentration of the Mg 2+ or Mn 2+ is about 20 mM. However, there is normally only about a 1-2 mM of these ions actually available in a cellular environment even though the cellular concentrations are usually in the range of 50- 100 mM. Thus, the available concentrations of Mg 2+ and Mn 2+ are a factor that limits the catalytic efficiency of a ribozyme. Methods for overcoming the limiting availability of these pores and therefore enhancing ribozyme activity are essential. Koizumi et al. , FEBS Lett. 239: 285-288 (1988), discuss the design of two ribozymes for site-specific cleavage of RNA. A UA site in an undecaribonucleotide was cleaved by a ribozyme consisting of two partially paired oligoribonucleotides with chain lengths of 19 and 15. The other ribozyme, which consists of 19-mer and a 13-mer, recognized a UC sequence at positions 42 and 43 of 5 S r NA. Haseloff and Gerlach, Nature 334: 585-59 (1988) , discuss the dissection of the RNA substrate and enzyme activities from a single self-cleaving domain from the (+) strand of the satellite RNA of tobacco ringspot virus (sTobRV) . Inspection of the separated substrate and ribozyme activities, in comparison with other naturally- occurring self-cleaving domains, led to a model for the design of oligoribonucleotides which posses new and highly sequence-specific endoribonuclease activities. This model was successfully tested by the design and construction of ribozymes targeted against three sites within the Tn9 chloramphenicol acetyl-transferase (CAT) messenger RNA sequence. Hampel and Tritz, Biochemistry 28.: 4929-4933 (1989), identified an RNA catalytic domain within the sequence of the 359 base long negative-strand satellite RNA of tobacco ringspot virus. The catalytic domain contains two minimal sequences of RNA, a 50 base catalytic RNA sequence, and a 14 base substrate RNA sequence. The catalytic complex of catalytic RNA/substrate RNA represents a structure not previously found in any RNA catalytic reaction. Hampel et al.. Nucleic Acids Res. 18.: 299-304 (1990) discuss the identification of the catalytic domain within the sequence of the negative strand of the satellite RNA of tobacco ringspot virus. Minimum energy RNA folding calculations predict a two dimensional model with four major helical regions which are supported by mutagenesis experiments. This model for the catalytic complex consists of a 50 base catalytic RNA and a 14 base substrate RNA folded together in a type of hairpin two dimensional structure. Part of the recognition region between the catalyst and substrate is two helices of 6 bases and 4 bases respectively. Catalytic activity remains when the bases in these two helices are changed but base pairing is maintained. Thus an appropriately engineered 'hairpin' catalyst is capable of cleaving heterologous RNA. Uhlenbeck, Nature, 32£: 596-600 (1987) describes the synthesis of two oligoribonucleotides that can combine to form a structure consistent with the consensus self- cleaving domain. Because rapid cleavage of one of the oligomers was observed only when the other was present, the domain was necessary and sufficient for cleavage. The properties of the cleavage reaction were studied in detail. Nearly complete cleavage occurred even with large excess of the oligomer that was cleaved. This indicates that the oligomer that is uncleaved can cycle in the reaction and therefore be considered to act as a catalyst in the cleavage of the other oligomer. Fedor and ϋhlenbeck, Proc. Natl. Acad. Sci. USA 87: 1668-1672 (1990) , analyzed the kinetics of cleavage for several hammerhead sequences to characterize the reaction mechanism and explore how nucleotides involved in substrate binding affect cleavage. Goodchild et al. , Arch. Biochem. Biophys. 263: 401-409 (1988) discusses the effects of a series of synthetic oligonucleotides (hybridons) complementary to the 5' non- coding regions of rabbit /S-globin mRNA on endogenous protein synthesis in a rabbit reticulocyte cell-free translation system. With highly purified hybridons inhibition was completely specific for beta globin. Mixtures of two oligonucleotides binding contiguously to the mRNA were more effective than either oligomer alone. Maher and Dolnick, Nucleic Acids Res. 16_: 3341-3358 (1988) report that antisense oligonucleotides containing either anionic diester or neutral methylphosphonate internucleoside linkages were prepared by automated synthesis, and subsequently compared for their ability to arrest translation of human dihydrofolate reductase (DHFR) mRNA in a nuclease treated rabbit reticulocyte lysate. In the case of oligodeoxyribonucleotides , tandem targeting of three 14-mers resulted in synergistic and complete selective inhibition of DHFR synthesis at a total oligomer concentration of 25 μM. Kutyavin et al, FEBS Lett. 238: 35-38 (1988) report that mono- and diphenazinium derivatives of oligonucleotides complementary to the DNA sequence adjacent to the target sequence of the addressed alkylation of DNA significantly enhance the extent and specificity of alkylation by p-(N-2-chloroethyl-N-methylamino(benzylamido) derivatives of the addressing oligonucleotides. SUMMARY OF THE INVENTION The present invention provides methods for increasing ribozyme catalytic activity without reducing specificity, which methods comprise reacting an RNA molecule with a ribozyme and a facilitator oligonucleotide. In the inventive method, the facilitator oligonucleotide hybridizes with a sequence in the target RNA that is either contiguous to or near a sequence in the target RNA to which the ribozyme hybridizes. The present invention further provides compositions comprising a ribozyme and an effective amount of a facilitator oligonucleotide. The invention also includes methods and compositions for treating humans and other mammals having various viral infections. The invention also provides methods for reducing the amount of magnesium (Mg + ) or manganese (Mn 2+ ) that is required by the ribozyme for catalytic cleavage of target RNA. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows the nucleotide sequences of substrate RNA Sγ) , ribozyme (R) and facilitator oligodeoxy- nucleotides F lf F 2 , F 3 , facilitator ribooligonucleotide F 4 and facilitator oligodeoxynucleotide F 5 . The site of cleavage of substrate is indicated by the arrow. Figure 2A is an autoradiograph showing the results of cleavage of radiolabelled substrate S ! by ribozyme R without facilitator oligonucleotide to give products P x and P 2 containing 20 and 13 nucleotides respectively. Figure 2B is an autoradiograph showing the results of cleavage of radiolabelled substrate S j by ribozyme R in the presence of facilitator oligonucleotide F j to give products P x and P 2 containing 20 and 13 nucleotides respectively. Figure 3 is a graph showing the effect of chain length on the rate of cleavage using facilitator oligonucleotides F j , F 2 , and F 3 and a control reaction with no facilitator oligonucleotide. Figure 4 is a graph comparing cleavage of substrate S using a facilitator that hybridizes to a sequence in the target substrate S γ that is contiguous to the S t sequence to which ribozyme R hybridizes (F 2 ) with cleavage by a facilitator that hybridizes to a sequence in S L that is spaced 3 nucleotides from the S j sequence to which ribozyme R hybridizes. Figure 5 is a graph comparing the cleavage of S L by R using deoxyoligonucleotide (F t ) or ribooligonucleotide (F 4 ) facilitators with a control reaction with no facilitator. Figure 6 is a graph comparing cleavage of S ! by R using a facilitator having a phosphorothioate backbone with cleavage by a control with no facilitator. Figure 7 shows the sequences of ribozymes R4 and R5 that differ only in the lengths of their flanking sequences (21 and 12 bases respectively) . Figure 8 is a graph comparing reactions catalyzed by R 4 and R 5 . The extent of reaction is shown as the ratio of product PI over R. Figure 9a shows the sequences of ribozyme R 5 and facilitator F j hybridized to substrate S j . Figure 9b shows the sequence of a ribozyme R 18 prepared by covalently linking facilitator F^ and ribozyme R 5 . Figure 10 is a graph comparing the rate of cleavage of subnstrate S 2 by R 5 alone, R 5 and Fj together, and R 18 alone. Figure 11 is a graph showing the effect of varying the Mg 2+ concentration and the effect of facilitator oligonucleotide on the rate of cleavage of substrate S j by ribozyme R 5 . DETAILED DESCRIPTION OF THE INVENTION The development of antiviral drugs based on RNA catalysts has been inhibited by the mutually limiting requirements of high specificity and RNA cleavage rate. Increased base pairing between a ribozyme and a substrate RNA has been shown to decrease the rate of RNA cleavage. In order for a ribozyme to discriminate between all RNAs in a cell, a ribozyme must form about 15 base pairs with the target. However, longer flanking sequences in ribozymes is related to decreased catalytic cleavage. It has been unexpectedly discovered that the rate of cleavage of substrate RNA by a ribozyme is enhanced by introducing an oligonucleotide into the system which hybridizes either near or immediately adjacent to the ribozyme. By facilitator oligonucleotide is meant an oligonucleotide that hybridizes with a sequence in the target RNA that is either contiguous to or near a sequence in the target RNA to which the ribozyme hybridizes. Thus, the facilitator oligonucleotide binds to a sequence in the target RNA that is spaced no more than about five nucleotides from the target RNA sequence to which the ribozyme hybridizes. It has also been unexpectedly discovered that the use of a facilitator oligonucleotide with a ribozyme reduces the amount of magnesium ion (Mg 2+ ) that is required by the ribozyme to σatalytically cleave target RNA sequences. The rate of cleavage of target RNA by a ribozyme is dramatically enhanced when target RNA is reacted with the ribozyme in the presence of a facilitator oligonucleotide. The facilitator oligonucleotides suitable for use in the instant invention may be either deoxyoligonucleotides or ribo-oligonucleotides. Furthermore, the facilitator oligonucleotide may be selected to bind to a sequence contiguous to the flanking sequence either at the 5' or the 3' side of the ribozyme. In addition, a combination of two facilitator oligonucleotides may be employed, where one facilitator is bound contiguously to the 3' flanking sequence and the other to the 5 r flanking sequence. Alternatively, a plurality of facilitators may be employed to catalyze ribozyme activity. For example, in a system employing three facilitators, two facilitators could bind contiguously to the 3' flanking sequence (a second facilitator would hybridize contiguous to a first facilitator hybridized adjacent the 3' flanking sequence of the ribozyme) , while a third facilitator could bind contiguously to the 5' flanking sequence. A variety of other combinations are possible. The facilitator oligonucleotides of the present invention typically comprise from about 5 to 50 nucleotides. More preferred facilitator oligonucleotides comprise from about 5 to 15 nucleotides. Particularly preferred facilitators according to the invention comprise about 13 nucleotides. Selection of a facilitator of a specific length is related to the length of the ribozyme flanking sequences. Preferred facilitator oligonucleotides containing phosphorothioate linkages comprise from about 15 to 30 nucleotides. Particularly preferred oligonucleotides containing phosphorothioate linkages comprise from about 20 to 25 nucleotides. The facilitator deoxynucleotides may be selected to have from about 5 to 50 nucleotides complementary to the RNA substrate sequence as well as additional nucleotides which are not complementary to the RNA sequence. The additional nucleotides not complementary to the RNA sequence do not hybirdize with the target RNA. The ribozymes of the invention are normally those that cleave related target RNA sequences. The specific facilitator oligonucleotides may be synthesized to hybridize with the desired RNA sequences such that the facilitator hybridizes with a sequence in the target RNA that is contiguous to a sequence in the target RNA to which the ribozyme hybridizes. As described here, the oligonucleotides can be synthesized on automated DNA synthesizers or from DNA templates. In addition, the facilitator oligonucleotides may be synthesized such that they do not hybridize to a sequence that is contiguous to the flanking sequence of the desired ribozyme. For example, the facilitator may be synthesized such that, when the ribozyme and facilitator oligonucleotide are bound to the substrate RNA, a small gap of from one to about five oligonucleotides exists between the ribozyme and the facilitator oligonucleotide. In other words, the facilitator oligonucleotide hybridizes with a sequence in the target RNA that is spaced about one to five oligonucleotides from the target RNA sequence to which the ribozyme hybridizes. The facilitator oligonucleotides may be synthesized and subsequently modified to include moieties which will influence the rate of substrate cleavage by ribozyme, increase uptake by cells, or increase resistance to degradation. The facilitator oligonucleotides may be prepared to contain substituted nucleotide analogs or modified nucleic acid backbones, resulting in chimeric oligonucleotides. The modifications may be either natural or synthetic. The oligonucleotides may optionally be chemically capped at either the 3' end or 5' end to yield a chemically capped oligonucleotide. The facilitator oligonucleotides may be modified to contain a nucleotide having a substituent on the oxygen at the 2'-position of the nucleotide; i.e., by introducing a 2'-O-substituted nucleotide into the facilitator. The substituent on the nucleotide 2 Λ -oxygen may be a lower alkyl group, lower alkenyl group, a phenyl alkyl group where the alkyl is lower alkyl, a phenyl alkenyl group where the alkenyl is lower alkenyl, an acyl group, or a phenylacyl group. Suitable synthetic methods for preparing various 2'-O-substituted nucleotides are disclosed by Iribarren et al., Proc. Natl. Acad. Sci. 87: 7747-7751 (1990); Sproat et al. , Nucleic Acids Res. JL9: 733-738 (1991); and Sproat et al. , Nucleic Acids Res. .18.: 41-49 (1989). Inclusion of 2'-O-alkylnucleotides stabilizes hybrids as well as increase resistance to degradation by nucleases. By increasing the number of bases of the substrate RNA hybridized near the cleavage site, facilitators permit use of faster acting ribozymes with shorter flanking sequences. Facilitators might be of dual benefit in also directing cleavage of the target RNA by endogenous ribonuclease H. While the method of the invention has been demonstrated using sequences from HIV-1 RNA, it is applicable to sequences from other sources. Thus, facilitator sequences may be chosen to enhance the catalytic rate of ribozymes that cleave target RNA that code for a variety of proteins that lead to disease. This technology is applicable to any disease situation where antisense nucleotides may be used. I.e.. the combination of facilitators and ribozyme may be employed in any disease situation where it is desired to inhibit the synthesis of a protein. In the methods of the invention, the facilitator oligonucleotides apparently do not dissociate from the target RNA and therefore do not appear to catalytically recycle. This apparent lack of dissociation thus requires employment of at least about a stoichiometric amount of facilitator oligonunucleotide. The ribozyme, however, does recycle and thus allows for use of only a catalytic amount of ribozyme in the invention. The present invention also includes compositions which comprise a ribozyme and an effective amount of a facilitator oligonucleotide. The invention further provides methods for treating mammals infected with a pathogenic organism such as a virus comprising administering to the mammal a ribozyme and a facilitator oligonucleotide in amounts effective to cleave target RNA, where the facilitator oligonucleotide hybridizes with a sequence in the target RNA that spaced no more than about five nucleotides from the target RNA to which the ribozyme hybridizes. For optimum activity, the facilitator should be used in an amount that is approximately stoichiometric with the amount of target RNA sequence while the ribozyme may be used in only a catalytic amount, e.g.. the ribozyme concentration may be about 5% of the facilitator concentration. In any treatment the compositions comprising the ribozyme and facilitator oligonucleotide must be administered to the mammal or individuals in a manner capable of delivering the oligonucleotide and ribozyme initially into the blood stream and subsequently into cells. Methods for preparing and administering compositions according to the invention that will be effective in vivo are easily determined. Antisense oligonucleotides very similar to facilitators and ribozymes are taken up by cells and can block the expression of target RNA. See e.g.. J. Goodchild in Oligonucleotides, Antisense Inhibitors of Gene Expression, pp 53-77, J. Cohen, editor, 1989, Macmillan Press, London; and Toulme in Antisense RNA and DNA. pp. 175-194, J.A.H. Murray, editor, 1992, Wiley-Liss, New York. It has been demonstrated that antisense oligonucleotides can block the expression of target RNA's in whole animals. J. Clin. Invest. $58.: 1190-1196 (Burch and Mahan 1991) . See e.g.. Antisense Research and Development JL: 349-350 (Whitesell et al., 1991); and Science 258: 1792-1795 (Kitajima et al., 1992). It is also well known that ribozymes able to cleave a target RNA in vitro, including HIV-1 RNA, also cleave it in cells with resulting inhibition of viral replication or of expression of the target RNA. See, J. Virol. .66.: 1432-144 (Dropulic et al., 1992); Nuc. Acids Res. .20: 4559-4565 (Taylor et al., 1992); Proc. Nat. Acad. Sci. USA 89: 10802-10806 (Ojwang et al., 1992); Gene, 117: 179-184 (Koizume et al., 1992); Journal of Virology, 65.: 5531-5534 (Weerasinghe et al., 1991) ; Proc. Nat. Acad. Sci. USA, 8.: 9139-9143 (Cameron and Jennings, 1989) ; EMBO Journal, 12.: 3861-3866 (Cotton and Birnstiel 1989) ; and Science, 247: 1222-1225 (Saver et al., 1990). The compositions of the invention may be administered parenterally, orally, by inhalation or spray or rectally in dosage unit formulations containing conventional non-toxic pharmaceutically acceptable carriers, adjuvants and vehicles. The term "parenteral" as used herein includes subcutaneous injections, intravenous, intramuscular, intrasternal injection or infusion techniques. The compositions of the invention would be provided in a pharmaceutical formulation comprising the composition and a pharmaceutically acceptable carrier. In order for the compositions to be suitable for oral administration, oligonucleotides and ribozymes must be resistant to nucleases. Such resistance to nucleases may be imparted to the oligonucleotides and ribozymes by, for example, internucleotide phosphate modifications. Modified internucleotide phosphates suitable for use in the facilitator oligonucleotides of the present invention include phosphorothioates, alkylphosphorothioates such as for example, methylphosphorothioates, alkylphosphonates such as, for example, methylphosphonates, phosphoramidates, and phosphotriesters. The amount of active composition that may be combined with the carrier materials to produce a single dosage form will vary depending upon the host treated and the particular mode of administration. It will be understood that the specific dose level for any particular patient will depend upon a variety of factors including the activity of the specific composition employed, the age, body weight, general health, sex, diet, time of administration, route of administration, severity of the particular disesse undergoing therapy. The compositions of the invention comprising ribozyme and facilitator oligonucleotides can be effectively administered intravenously or subcutaneously using doses of from about 0.1 mg/kg to about 50 mg/kg to yield facilitator concentrations in the patient of from about 0.01 μM to about 100 μϋ. One skilled in the art will recognize that modifications may be made in the present invention without deviating from the spirit or scope of the invention. The invention is illustrated further by the following examples which are not to be construed as limiting the invention or scope of the specific procedures described herein. Example l 1. Preparation of RNA Substrate A synthetic RNA substrate strand (S x ) was prepared to correspond to the sequence 146-173 in HIV-1 RNA; the sequence of which is shown in Figure 1. This RNA substrate strand was transcribed from synthetic DNA templates following a method described by Milligan and Uhlenbeck, Nucleic Acids Res. 15: 8783-8798 (1987), in a reaction containing TrisΗCl (40 mM, pH 8.1), MgCl 2 (6 mM) , spermidine (1 mM) , dithiothreitol (50 mM) , bovine serum albumin (50 μg per ml) , inorganic pyrophosphatase (4 units per ml) , T7 RNA polymerase (4000 units per ml) and four ribonucleotide 5'-triphosphates (1 μM each) supplemented with α- 32 P-UTP (3000 Ci/mmol) . After incubation at 37°C for 2 hours, the RNA was purified by electrophoresis in 10% polyaerylamide gels containing 8 M urea. The radiolabeled RNA was quantitated using the specific activity of the incorporated 32 P. 2. Preparation of Hammerhead Ribozyme A hammerhead ribozyme (R) designed to cleave RNA substrate strand S t was prepared. The sequence of ribozyme R is shown in Figure 1. The hammerhead ribozyme was prepared by automated chemical synthesis using standard phosphoramidite reagents. Products were purified by electrophoresis in 15% polyacrylamide gels containing 8M urea, eluted by crush and soak in 0.5M ammonium acetate, desalted and quantitated by UV absorption. Hammerhead ribozymes R 4 and R 5 , the sequence of each of which is shown in Figue 7, were designed to cleave a substrate strand and prepared using essentially the procedure described above for ribozyme R. 3. Preparation of Facilitator and Control Oligonucleotides Facilitator oligonucleotides F j , F 2 , and F 3 were prepared to contain 13, 10, and 6 nucleotides respectively, and to hybridize to substrate S contiguously with ribozyme R. Facilitator oligoribonucleotide F 4 was prepared with the same sequence as F j . In addition, a control oligonucleotide having a random sequence was synthesized. The sequences of oligonucleotides F lf F 2 , F 3 , and F 4 are shown in Figure 1. Both ribo- and deoxyoligonucleotides were prepared by automated chemical synthesis utilizing essentially the same procedures set forth in part 2 of this Example. Facilitator oligonucleotide F 5 was prepared using essentially the same procedure as facilitators F j -F 4 and contained 10 nucleotides. The sequence of F 5 is shown in Figure 1. Example 2 Preparation of Ribozymes R 18 and R 5 A ribozyme consisting of a 35 nucleotide sequence (R 5 ) was prepared essentially according to the procedure set forth in part 2 of Example 1 above. A 48 nucleotide ribozyme, R 18 , was prepared by covalently coupling R 5 with facilitator F j (prepared above) . The sequences of ribozymes R 5 , R 18 and facilitator, F j , are shown in Figures 9a and 9b. Example 3 Cleavage of Substrate RNA The cleavage of substrate RNA by ribozyme R was studied both with and without facilitator oligo F j . The cleavage of substrate RNA gave products P x and P 2 having chain lengths expected from cleavage at the site indicated in Figure 1. The cleavage reactions were run as follows: a solution (45 μl) containing substrate (13.4 μM) , ribozyme (0.67 μM) and facilitator where appropriate (20 μM) in 50 mM TrisΗCl (pH 7.4) was brought to 37°C. Reaction was initiated by the addition of MgCl 2 (5 μL, 200 mM) . After times of 0.5, 1, 2, 5, and 10 minutes, aliquots of 5 μL were added to 15 μl of saturated urea:200 mM EDTA (1:1) and cooled to about -70°C with dry ice to stop the reaction. The samples were then denatured by heating in formamide loading buffer at 90°C for 3 minutes and subsequently analyzed alongside molecular weight markers by electrophoresis in 15% polyacrylamide gel containing 7M urea. The products were autoradiographed. The autoradiographs are shown in Figure 2. Panel A shows the results of the cleavage reaction without any facilitator oligonucleotide and Panel B shows the results of cleavage with facilitator oligonucleotide Fi- Example 4 Relation of Facilitator Length to Ribozyme Activity Cleavage of substrate RNA by ribozyme R was determined in the presence of facilitator oligonucleotides (Fj, F 2 , F 3 , and F 4 ) of varying length. Cleavage reactions were run under conditions substantially similar to those employed in Example 2 above. Products and starting materials were quantitated for each time point. Autoradiograph gels were sliced and the materials on the slices quantitated by scintillation counting. The results of this experiment are graphically shown in Figure 3. Cleavage with no facilitator reached about 94% completion after about 160 minutes. The facilitator of 13 deoxynucleotides significantly reduced reaction half life. Table 1 shows the time required for ribozyme to cleave 10 equivalents of substrate at 37°C. The longest facilitator, F j , produced this half life time from 10 minutes to 1.3 minutes. The effects of facilitators F j -F 3 were inversely related to their lengths. A control oligonucleotide of the same length as F j had no effect on the rate. In a separate experiment. Example 7, it was found that oligodeoxynucleotide F j was more effective at catalyzing ribozyme activity than o1igoribonucleotide F 4 having the same sequence. TABLE 1 Half-Lives of Substrate in the Presence of Ribozyme and Facilitators Starting concentrations of substrate (μM) Example 5 Relation of Ribozyme Length and Activity and Facilitator to Cleavage Rate The rate of cleavage of target RNA (S) by ribozymes R 5 and R J8 was compared. Cleavage reactions were run as described in Example 3. The following three reactions were performed: 1. Cleavage with Ribozyme R 5 and facilitator F 1 . 2. Cleavage with Ribozyme R 5 alone. 3. Cleavage with Ribozyme R 18 alone. The results are shown in Figure 10. The ribozyme and separate facilitator cleaved target RNA at a much faster rate than the single ribozyme although the total number of base pairs formed with the target was the same in both cases. Example 6 Cleavage by Ribozyme and Facilitator spaced from ribozyme The cleavage of substrate RNAfS^ was studied using ribozyme (R) and a facilitator F 5 that hybridizes to a sequence in S j that is spaced 3 nucleotides from the S j sequence to which R hybridizes. The cleavage reactions were run essentially as described above in Example 3. Each reaction contained 20 equivalents of S j and 30 of facilitator relative to R. A control reaction contained no facilitator. The initial concentration of S was 2.7 μM and reactions were performed in 50 mM Tris, pH 7.4 and 20 mM MgCl 2 at 37°C. The results are shown in Figure 4. Example 7 Cleavage of Substrate by Ribozyme in the Presence of Facilitator Comprising Ribooligonucleotides and Deoxyoligonucleotides The rates of cleavage in the presence of deoxyoligonucleotide (F j ) and ribooligonucleotide (F 4 ) facilitator, and a control with no facilitator were studied. Reactions were performed essentially as described above in Example 6 using an initial substrate S j concentration of 1.6 μM. The results are shown in Figure 5. Example 8 Cleavage by Ribozyme in the presence of facilitator having a phosphorothioate backbone Cleavage of substrate RNA was studied using a facilitator having a phosphorothioate linkage as part of its backbone and compared to a control reaction having no facilitator. The reactions were run essentially as described in Example 6 at a temperature of 22°C. The results are shown in Figure 6. Example 9 Relation between Ribozyme length and Activity The rate of cleavage by ribozyme R 4 (21 nucleotides) was compared to that of ribozyme R 5 (12 nucleotides) using reaction conditions essentially as set forth in Example 6, above. The initial concentrations were: 19 nM ribozyme and 190 nM substrate. Results are shown in Figure 8 as the ratio of the concentration of product, P x over R. Exa ple ιo Relation of Facilitator to [Mg 2+ 1 Required for Cleavage The rate of substrate (S j ) cleavage by ribozyme R 5 was studied with and without facilitator at various concentrations of Mg 2+ . The reactions were run essentially as described above in Example 6, but at different concentrations of Mg 2+ . The results are shown in Figure 11. From the foregoing, it will appreciated that although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit or scope of the invention.

Claims: WHAT IS CLAIMED IS: 1. A method for increasing the catalytic activity of a ribozyme comprising reacting a target RNA molecule with the ribozyme and a facilitator oligonucleotide, where the facilitator oligonucleotide hybridizes with a sequence in the target RNA that spaced no more than about five nucleotides from the target RNA to which the ribozyme hybridizes. 2. A method according to Claim 1, wherein the facilitator oligonucleotide comprises from about 5 to about 50 nucleotides. 3. A method according to Claim 2, wherein the facilitator oligonucleotide comprises from about 5 to about 15 nucleotides. 4. A composition comprising a ribozyme and an effective amount of a facilitator oligonucleotide. 5. A composition according to Claim 4, wherein the facilitator oligonucleotide hybridizes with a sequence in the target RNA that spaced no more than about five oligonucleotides from the target RNA to which the ribozyme hybridizes. 6. A composition according to Claim 5, wherein the facilitator oligonucleotide comprises from about 5 to about 50 nucleotides. 7. A composition according to Claim 6, wherein the facilitator oligonucleotide comprises from about 5 to about 15 nucleotides. 8. A facilitator oligonucleotide having the structure AGGGTC that binds to a sequence in a target RNA that is contiguous to a sequence in the target RNA to which the ribozyme hybridizes. 9. A facilitator oligonucleotide having the structure AGGGTCTGTT that binds to a sequence in a target RNA that is contiguous to a sequence in the target RNA to which the ribozyme hybridizes. 10. A facilitator oligonucleotide having the structure AGGTCTGTTTTC that binds to a sequence in a target RNA that is contiguous to a sequence in the target RNA to which the ribozyme hybridizes. 11. A method according to Claim 1, wherein the facilitator oligonucleotide comprises a modified internucleotide phosphate. 12. A method according to Claim 11, wherein the modified internucleotide phosphate is selected from the group consisting of phosphorothioates, alkylphosphorothioates, alkylphosphonates, phosphoramidates , and phosphotriesters. 13. A composition according to Claim 4, wherein the facilitator oligonucleotide comprises a modified internucleotide phosphate. 14. A composition according to Claim 13, wherein the modified internucleotide phosphate comprises a phosphorothioate, methylphosphonate, phosphoramidate, or phosphotriester. 15. A method for treating a mammal infected with a pathogenic organism comprising administering to the mammal a ribozyme and a facilitator oligonucleotide in an amount effective to cleave target RNA, where the facilitator oligonucleotide hybridizes with a sequence in the target RNA that spaced no more than about five nucleotides from the target RNA to which the ribozyme hybridizes. 16. A method according to Claim 15, wherein the facilitator oligonucleotide is administered in an amount that is stoichiometric with the target RNA. 17- A method for reducing the concentration of Mg 2+ and Mn 2+ required by a ribozyme for catalytic cleavage of target RNA comprising treating the target RNA with the ribozyme and a facilitator oligonucleotide that hybridizes with a sequence in target RNA that is spaced no more than about five nucleotides from the target RNA sequence to which the ribozyme hybridizes. 18. A method for cleaving target RNA with a ribozyme comprising reducing the concentration of an ion selected from the group consisting of Mg 2+ and Mn 2+ by treating the target RNA with the ribozyme in the presence of a facilitator oligonucleotide that hybridizes with a sequence in target RNA that is spaced no more than about five nucleotides from the target RNA sequence to which the ribozyme hybridizes. 19. A method for inhibiting the replication of target retroviral RNA comprising reacting the target RNA with a ribozyme and a facilitator oligonucleotide that hybridizes with a sequence in target RNA that is spaced no more than about five nucleotides from the target RNA sequence to which the ribozyme hybridizes.

Inventors: GOODCHILD JOHN, GOODCHILD, JOHN
Applicants: WORCESTER FOUND EX BIOLOGY, WORCESTER FOUNDATION FOR EXPERIMENTAL BIOLOGY
Application year: 1993
Main classification: C12N9
IPC codes: A61K31, A61K38, A61P31, C07H21, C07K14, C12N9, C12N15