Summary auto-generated
This 1983 review article examines cloning vectors derived from animal viruses for introducing and expressing foreign genes in eukaryotic cells. The author discusses how prokaryotic vectors have revolutionized molecular biology, but studying gene function requires returning cloned genes to their natural cellular environment. Since eukaryotic cells lack well-defined plasmid systems, animal viruses provide suitable vector bases. The review covers several viral systems: SV40 vectors (limited by small genome size and strict packaging constraints); adenovirus vectors (larger genome accommodating bigger inserts); retroviruses (offering intact integration, wide host range, and natural transduction capability); and emerging systems using herpes simplex and vaccinia viruses. The author emphasizes advantages of episomal replication vectors like bovine papillomavirus-1 (BPV-1) and SV40-based COS cell systems, which avoid packaging constraints and enable stable cell line construction. A critical requirement is dominant selectable markers—genes conferring selectable phenotypes in any cell type—exemplified by bacterial resistance genes expressed from viral promoters. The review highlights that efficient DNA transfer into eukaryotic cells, achieved through calcium phosphate transfection or protoplast fusion, remains essential for vector utility.
Key findings
- Animal viruses provide suitable vector backbones for eukaryotic gene cloning because they contain defined control regions and replication elements absent in eukaryotic cells
- SV40, adenovirus, and retrovirus vectors each offer distinct advantages: SV40 for well-characterized early/late promoters, adenoviruses for larger inserts, and retroviruses for stable integration and efficient expression
- Episomal replication systems (BPV-1 and COS cells) overcome packaging constraints and enable construction of stable cell lines expressing foreign genes
- Dominant selectable markers derived from bacterial resistance genes are essential for identifying transfected cells in any cell type
- Efficient DNA transfer methods such as calcium phosphate transfection and protoplast fusion are critical limiting factors in establishing functional eukaryotic cloning systems
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Abstract
Conclusions: The examples discussed above show clearly that the development of vectors for use in eukaryotic cells is presently proceeding very rapidly. Knowledge gained from the use of one type of vector defines the design criteria for the next type and thus many systems become obsolete before they are fully developed. Some future work can be predicted with reasonable certainty. The vast majority of future vectors will incorporate dominant selectable markers and regulatable promoters and we can expect to see vectors containing several different origins of DNA replication so that their replication can be controlled in several ways. In parallel with these refinements will occur the development of eukaryotic vectors suitable for the primary cloning of genomic DNA or cDNA. This will be of the greatest importance as it will allow the immunological or phenotypic recognition of genes by virtue of their expression in eukaryotic cells, thus facilitating the isolation of eukaryotic genes which can not be detected by the techniques available for screening prokaryotic clones. The use of such vector systems will surely be a central feature of all future work in eukaryotic molecular biology.