Difference between revisions of "Part:BBa K404125"

Producing recombinant virus particles for therapeutical applications is, besides specific cell targeting, purification and quantification assays of AAV-2, one intention of the Virus Construction Kit provided by the iGEM team Freiburg_Bioware 2010. For obtaining a modular toolkit, the complex biological system of the Adeno-associated virus serotype 2 was examined by an exhaustive literature search. Subsequently, the essential components for AAV-2 particle production were extracted and redesigned to match the iGEM standard.

The provided tripartite system is independent of a superinfection  of Adeno- or herpes simplex viruses since the genes encoding the required helper-proteins are co-transfected. Inside the eukaryotic host cell, the DNA sequence containing the inverted terminal repeats (ITRs) is extracted and later encapsidated into the preformed capsids after production of single-stranded DNA. Consequently, this plasmid is known as the vector plasmid (pGOI). Promoter, beta-globin intron and the hGH terminator signal are flanked by the ITRs (ITRs, BBa_K404100 and BBa_K404101) and regulate transgene expression. The vector plasmid containing the desired gene of interest is cotransfected with the RepCap plasmid (BBa_K404001, BBa_K404002 or BBa_K404003) and the pHelper plasmid. To obtain the fully assembled vector plasmid, several assembly steps have to be performed. The gene of interest (GOI) cytosine deaminase (XXX) was inserted into the transgene expression cassette and its biological activity was test in cell culture. In E. coli, Cytosine Deaminase (CD) (EC 3.5.4.1) is encoded by codA. The protein plays a crucial role in nucleotide synthesis since it catalyzes the deamination of cytosine to uracil (Danielsen et al. 1992).
In eukaryotic cells, expression of this protein can be used to convert the non-toxic prodrug 5-fluorocytosine to the toxic compound 5-fluorouracil.

The presence of this nucleotide analogue in the target cell blocks the synthesis of thymidine by inhibition of the essential enzyme thymidylate synthase, therefore leading to cell death. Furthermore, this construct contains the tumor-specific phTERT promoter, providing another layer of specificity and safety to the recombinant viral vector system. Telomerase activation is a critical step in human tumorigenesis and about 85 ± 90% of several human tumors show telomerase activity. In most somatic cells, the phTERT promoter is inactive. This prevents expression of the hTERT protein subunit and renders the healthy tissue telomerase negative.