Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Preparing compound containing saccharide radical
Reexamination Certificate
1998-09-23
2001-08-28
LeGuyader, John L. (Department: 1635)
Chemistry: molecular biology and microbiology
Micro-organism, tissue cell culture or enzyme using process...
Preparing compound containing saccharide radical
C435S091310, C435S320100, C435S325000, C435S455000, C536S023100
Reexamination Certificate
active
06280978
ABSTRACT:
INTRODUCTION
The present invention provides methods and compositions for generating novel nucleic acid molecules through targeted spliceosomal trans-splicing. The compositions of the invention include pre-trans-splicing molecules (PTMs) designed to interact with a natural target precursor messenger RNA molecule (target pre-mRNA) and mediate a trans-splicing reaction resulting in the generation of a novel chimeric RNA molecule (chimeric RNA). The PTMs of the invention are genetically engineered so as to result in the production of a novel chimeric RNA which may itself perform a function, such as inhibiting the translation of the RNA, or that encodes a protein that complements a defective or inactive protein in a cell, or encodes a toxin which kills specific cells. Generally, the target pre-mRNA is chosen as a target because it is expressed within a specific cell type thus providing a means for targeting expression of the novel chimeric RNA to a selected cell type. The invention further relates to PTMs that have been genetically engineered for the identification of exon/intron boundaries of pre-mRNA molecules using an exon tagging method. In addition, PTMs can be designed to result in the production of chimeric RNA encoding for peptide affinity purification tags which can be used to purify and identify proteins expressed in a specific cell type. The methods of the invention encompass contacting the PTMs of the invention with a target pre-mRNA under conditions in which a portion of the PTM is trans-spliced to a portion of the target pre-mRNA to form a novel chimeric RNA molecule. The methods and compositions of the invention can be used in cellular gene regulation, gene repair and suicide gene therapy for treatment of proliferative disorders such as cancer or treatment of genetic, autoimmune or infectious diseases. The methods and compositions of the invention can also be used to map intron-exon boundaries and to identify novel proteins expressed in any given cell.
BACKGROUND OF THE INVENTION
DNA sequences in the chromosome are transcribed into pre-mRNAs which contain coding regions (exons) and generally also contain intervening non-coding regions (introns). Introns are removed from pre-mRNAs in a precise process called splicing (Chow et al., 1977, Cell 12:1-8; and Berget, S. M. et al., 1977, Proc. Natl. Acad. Sci. USA 74:3171-3175). Splicing takes place as a coordinated interaction of several small nuclear ribonucleoprotein particles (snRNP's) and many protein factors that assemble to form an enzymatic complex known as the spliceosome (Moore et al., 1993, in The RNA World, R. F. Gestland and J. F. Atkins eds. (Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.); Kramer, 1996, Annu. Rev. Biochem., 65:367-404; Staley and Guthrie, 1998, Cell 92:315-326).
Pre-mRNA splicing proceeds by a two-step mechanism. In the first step, the 5′ splice site is cleaved, resulting in a “free” 5′ exon and a lariat intermediate (Moore, M. J. and P. A. Sharp, 1993, Nature 365:364-368). In the second step, the 5′ exon is ligated to the 3′ exon with release of the intron as the lariat product. These steps are catalyzed in a complex of small nuclear ribonucleoproteins and proteins called the spliceosome.
The splicing reaction sites are defined by consensus sequences around the 5′ and 3′ splice sites. The 5′ splice site consensus sequence is AG/GURAGU (where A=adenosine, U=uracil, G=guanine, C=cytosine, R=purine and/=the splice site). The 3′ splice region consists of three separate sequence elements: the branch point or branch site, a polypyrimidine tract and the 3′ splice consensus sequence (YAG). These elements loosely define a 3′ splice region, which may encompass 100 nucleotides of the intron upstream of the 3′ splice site. The branch point consensus sequence in mammals is YNYUR
A
C (where N=any nucleotide, Y=pyrimidine). The underlined A is the site of branch formation (the BPA=branch point adenosine). The 3′ splice consensus sequence is YAG/G. Between the branch point and the splice site there is usually found a polypyrimidine tract, which is important in mammalian systems for efficient branch point utilization and 3′ splice site recognition (Roscigno, R., F. et al., 1993, J. Biol. Chem. 268:11222-11229). The first YAG trinucleotide downstream from the branch point and polypyrimidine tract is the most commonly used 3′ splice site (Smith, C. W. et al., 1989, Nature 342:243-247).
In most cases, the splicing reaction occurs within the same pre-mRNA molecule, which is termed cis-splicing. Splicing between two independently transcribed pre-mRNAs is termed trans-splicing). Trans-splicing was first discovered in trypanosomes (Sutton & Boothroyd, 1986, Cell 47:527; Murphy et al., 1986, Cell 47:517) and subsequently in nematodes (Krause & Hirsh, 1987, Cell 49:753); flatworms (Rajkovic et al., 1990, Proc. Nat'l. Acad. Sci. USA, 87:8879; Davis et al., 1995, J. Biol. Chem. 270:21813) and in plant mitochondria (Malek et al., 1997, Proc. Nat'l. Acad. Sci. USA 94:553). In the parasite
Trypanosoma brucei,
all mRNAs acquire a splice leader (SL) RNA at their 5′ termini by trans-splicing. A 5′ leader sequence is also trans-spliced onto some genes in
Caenorhabditis elegans.
This mechanism is appropriate for adding a single common sequence to many different transcripts.
The mechanism of trans-splicing, which is nearly identical to that of conventional cis-splicing, proceeds via two phosphoryl transfer reactions. The first causes the formation of a 2′-5′ phosphodiester bond producing a ‘Y’ shaped branched intermediate, equivalent to the lariat intermediate in cis-splicing. The second reaction, exon ligation, proceeds as in conventional cis-splicing. In addition, sequences at the 3′ splice site and some of the snRNPs which catalyze the trans-splicing reaction, closely resemble their counterparts involved in cis-splicing.
Trans-splicing may also refer to a different process, where an intron of one pre-mRNA interacts with an intron of a second pre-mRNA, enhancing the recombination of splice sites between two conventional pre-mRNAs. This type of trans-splicing was postulated to account for transcripts encoding a human immunoglobulin variable region sequence linked to the endogenous constant region in a transgenic mouse (Shimizu et al.,1989, Proc. Nat'l. Acad. Sci. USA 86:8020). In addition, trans-splicing of c-myb pre-RNA has been demonstrated (Vellard, M. et al. Proc. Nat'l. Acad. Sci. 89:2511-2515) and more recently, RNA transcripts from cloned SV40 trans-spliced to each other were detected in cultured cells and nuclear extracts (Eul et al., 1995, EMBO. J. 14:3226). However, naturally occurring trans-splicing of mammalian pre-mRNAs is thought to be an exceedingly rare event. The reaction mechanism of trans-splicing is believed to be nearly identical to conventional cis-splicing. It proceeds via the formation of a 2′-5′ phosphodiester bond producing a ‘Y’ shaped branched intermediate (equivalent to the lariat intermediated in cis-splicing).
In vitro trans-splicing has been used as a model system to examine the mechanism of splicing by several groups (Konarska & Sharp, 1985, Cell 46:165-171 Solnick, 1985, Cell 42:157; Chiara & Reed, 1995, Nature 375:510; Pasman and Garcia-Blanco, 1996, Nucleic Acids Res. 24:1638). Reasonably efficient trans-splicing (30% of cis-spliced analog) was achieved between RNAs capable of base pairing to each other, splicing of RNAs not tethered by base pairing was further diminished by a factor of 10. Other in vitro trans-splicing reactions not requiring obvious RNA-RNA interactions among the substrates were observed by Chiara & Reed (1995, Nature 375:510), Bruzik J. P. & Maniatis, T. (1992, Nature 360:692) and (Bruzik J. P. and Maniatis, T., 1995, Proc. Nat'l. Acad. Sci. USA 92:7056-7059). These reactions occur at relatively low frequencies and require specialized ele
Garcia-Blanco Mariano A.
Mitchell Lloyd G.
Intronn Holdings LLC
Larson Thomas G.
LeGuyader John L.
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