Abstract:
Disclosed herein are nucleic acid sequences which support episomal replication in a mammalian cell. These nucleic acid sequences, which have a length of less than 3 kb, include (a) an OriP sequence and (b) an EBNA1 sequence operably linked to a promoter.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims benefit of the filing date of U.S. Provisional Application No. 60/050,206, filed Jun. 19, 1997, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Epstein-Barr virus (EBV) is a human herpes virus with a latent phase characterized by stable episomal propagation of a circular form of the viral DNA. Two discontinuous DNA elements are required for latent phase replication, the cis-acting origin of replication, OriP, and the Epstein-Barr Nuclear Antigen 1 (EBNA1), the sole virally encoded protein necessary for replication (Yates et al., Proc. Natl. Acad. Sci. USA 81:3806-10, 1984; Yates et al., Nature 313:812-5, 1985). Most EBV vectors are very large, on the order of 10 kb or more (without insert), because of the large size of the EBNA1 and OriP segments. The size of most existing EBV EBNA1 and OriP segments has interfered with the development of improved expression vectors and the creation of compact gene expression and persistence cassettes which can be embedded in other gene delivery vehicles, such as retroviruses or adenoviruses. 
     SUMMARY OF THE INVENTION 
     In general, the invention features a nucleic acid sequence which supports episomal replication in a mammalian cell. This nucleic acid sequence includes (a) an OriP sequence (for example, an OriP fragment) and (b) an EBNA1 sequence (for example, an EBNA fragment) operably linked to a promoter, and the nucleic acid sequence has a length of less than 3 kb, preferably less than 2 kb, and, most preferably, less than 1.8 kb. 
     In preferred embodiments, the OriP sequence includes approximately residues 1-495 of SEQ ID NO: 1; the EBNA1 sequence includes approximately residues 627-1718 of SEQ ID NO: 1; the nucleic acid sequence further includes a polyadenylation consensus sequence (for example, approximately the sequence of SEQ ID NO: 2); and the promoter is a viral promoter. 
     In related aspects, the invention also features vectors and cells (for example, mammalian cells, and preferably human cells) that include such nucleic acid sequences. 
     By &#34;an OriP fragment&#34; is meant a nucleic acid sequence which provides for OriP-mediated episomal replication but which is deleted for at least a portion of the nucleic acid sequence associated with the full-length origin. 
     By &#34;an EBNA fragment&#34; is meant a nucleic acid sequence which encodes an EBNA protein which provides for episomal replication but which is deleted for at least a portion of the nucleic acid sequence associated with the full-length viral gene. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B is the sequence of a shortened EBV OriP and EBNA-1 cassette. 
     FIG. 2 is the sequence of a compact synthetic bidirectional polyadenylation sequence which may be used in conjunction with a compact EBV replicon. 
    
    
     DETAILED DESCRIPTION 
     After extensive deletion and mutagenesis, it has been found possible to embed the cis- and trans-acting functions necessary for EBV episomal replication into a fragment of less than 2 kb. In particular, an exemplary fragment of 1748 base pairs which acts as a compact EBV replicon is shown in FIG. 1 (SEQ ID NO: 1). This fragment contains all sequences needed for efficient expression of the EBNA-1 protein, with the exception of a polyadenylation consensus sequence. The fragment is a Bgl2 to BamH1 segment which contains the OriP element between residues 1 and 495, a modified promoter from the Herpes simplex virus 1 thymidine kinase gene between residues 496 to 616, and the coding sequence for a deleted and modified EBNA1 gene between residues 627 and 1718. Plasmid vectors based on this sequence replicate as episomes in the nucleus of transfected cells of nonrodent origin (Yates et al., Nature 313:812-5, 1985). 
     To minimize overall sequence length, the above fragment was designed to be inserted upstream from a bidirectional polyadenylation sequence in an appropriate vector. An example of a compact synthetic bidirectional polyadenylation sequence is provided in FIG. 2 (SEQ ID NO: 2). 
     Compact EBV replicons find use in gene therapy vectors, for example, in gene delivery vehicles such as expression vectors. 
     Other embodiments are within the claims. 
     
         __________________________________________________________________________#             SEQUENCE LISTING  - -  - - &lt;160&gt; NUMBER OF SEQ ID NOS: 2  - - &lt;210&gt; SEQ ID NO 1 &lt;211&gt; LENGTH: 1748 &lt;212&gt; TYPE: DNA &lt;213&gt; ORGANISM: Epstein Barr Virus  - - &lt;400&gt; SEQUENCE: 1  - - agatctcctt gggaggtggc ggcatatgca aaggatagca ctcccactct ac -#tactgggt     60   - - atcatatgct gactgtatat gcatgaggat agcatatgct acccggatac ag -#attaggat    120   - - agcatatact acccagatat agattaggat agcatatgct acccagatat ag -#attaggat    180   - - agcctatgct acccagatat aaattaggat agcatatact acccagatat ag -#attaggat    240   - - agcatatgct acccagatat agattaggat agcctatgct acccagatat ag -#attaggat    300   - - agcatatgct acccagatat agattaggat agcatatgct atccagatcg ct -#gttcctta    360   - - ggaccctttt actaacccta attcgatagc atatgcttcc cgttgggtaa ca -#tatgctat    420   - - tgaattaggg ttagtctgga tagtatatac tactacccgg gaagcatatg ct -#acccgttt    480   - - agggttaata agggggatct ccccgcccag cgtcttgtca ttggcgaact cg -#aacacgca    540   - - gatgcagtcg gggcggcgcg gtcccaggtc cacttcgcat attaaggtga ca -#cgcgcggc    600   - - ctcgaacaca gctgcaggcc gccatcatgg cacatggacg aggacgggga ag -#aggacgag    660   - - gacgaggagg cggaagacca ggagccccgg gcggctcagg atcagggcca ag -#acatagag    720   - - atggtgtccg gagaccccaa aaacgtccaa gttgcattgg ctgcaaaggg ac -#ccacggtg    780   - - gaacaggagc aggagcagga gcgggagggg caggagcagg aggtggaggc cg -#gggtcgag    840   - - gaggcagtgg aggccggggt cgaggaggta gtggaggccg gggtcgagga gg -#tagtggag    900   - - gccgccgggg tagaggacgt gaaagagcca gggggggaag tcgtgaaaga gc -#caggggga    960   - - gaggtcgtgg acgtggagaa aagaggccca ggagtcccag tagtcagtca tc -#atcatccg   1020   - - ggtctccacc gcgcaggccc cctccaggta gaaggccatt tttccaccct gt -#aggggaag   1080   - - ccgattattt tgaataccac caagaaggcg gcccagatgg tgagcctgac gt -#gcccccgc   1140   - - gcagcggggg tcagggtgat ggaggcaggc gcaaaaaagg agggtggttt gg -#aaagcatc   1200   - - gtggtcaagg aggttccaac ccgaaatttg agaacattgc agaaggttta ag -#agctctcc   1260   - - tggctaggag tcacgtagaa aggactaccg acgaaggaac ttgggtcgcc gg -#tgtgttcg   1320   - - tatatggagg tagtaagacc tccctttaca acctaaggcg aggaactgcc ct -#tgctattc   1380   - - cacaatgtcg tcttacacca ttgagtcgtc tcccctttgg aatggcccct gg -#acccggcc   1440   - - cacaacctgg cccgctaagg gagtccattg tctgttattt catggtcttt tt -#acaaactc   1500   - - atatatttgc tgaggttttg aaggatgcga ttaaggacct tgttatgaca aa -#gcccgctc   1560   - - ctacctgcaa tatcagggtg actgtgtgca gctttgacga tggagtagat tt -#gcctccct   1620   - - ggtttccacc tatggtggaa ggggctgccg cggagggtga tgacggagat ga -#cggagatg   1680   - - aaggaggtga tggagatgag ggtgaggaag ggcaggagtg atgtaacttg tt -#aggagacg   1740   - - atggatcc                - #                  - #- #        1748   - -  - - &lt;210&gt; SEQ ID NO 2  &lt;211&gt; LENGTH: 103  &lt;212&gt; TYPE: DNA  &lt;213&gt; ORGANISM: Artificial Sequence  &lt;220&gt; FEATURE:  &lt;223&gt; OTHER INFORMATION: Bidirectional polyadenylation - #sequence  - - &lt;400&gt; SEQUENCE: 2  - - ggatccaaaa ataaaataaa ataaaaatta aaaaaaaagt gttgtgtcac ac -#aaaaaacc     60   - - aacacacatt tttttttgtt tttataaacc ctttattgtt aac    - #- #103__________________________________________________________________________