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The PA317 cell line was derived from TK- NIH/3T3 cells by cotransfection with packaging construct DNA (pPAM3) carried in pBR322 and the herpes simplex virus thymidine kinase (TK) gene carried in pBR322.

Cells shipped from the ATCC have been selected in medium containing 0.03 mM hypoxanthine, 0.001 mM amethopterin (methotrexate), and 0.02 mM thymidine prior to freezing, and should be grown in HT medium for 4 days after receipt. After this, the cells are stable for at least 1 month in the absence of further selection.

Introduction of retroviral vectors into these cells, by infection or by transfection, results in production of retrovirus virions with an amphotropic host range that are capable of infecting cells of many mammalian species.

The percentage of PA317 cells that are capable of packaging retroviral vectors decreases slowly with continued passaging of the cell line, presumably due to the loss of the transfected DNA used to create the line.

Brief selection (about 5 days) in medium containing 0.03 mM hypoxanthine, 0.001 mM amethopterin (methotrexate), and 0.02 mM thymidine will select for cells that retain the packaging function. After selection, the cells should be grown in HT medium (0.03 mM hypoxanthine, 0.02 mM thymidine) for 4 days to dilute any residual amethopterin.

1. Remove and discard culture medium.
2. Briefly rinse the cell layer with 0.25% (w/v) Trypsin-0.53mM EDTA solution to remove all traces of serum which contains trypsin inhibitor.
3. Add 2.0 to 3.0 mL of Trypsin-EDTA solution to flask and observe cells under an inverted microscope until cell layer is dispersed (usually within 5 to 15 minutes).
   Note: To avoid clumping do not agitate the cells by hitting or shaking the flask while waiting for the cells to detach. Cells that are difficult to detach may be placed at 37°C to facilitate dispersal.
4. Add 6.0 to 8.0 mL of complete growth medium and aspirate cells by gently pipetting.
5. Add appropriate aliquots of the cell suspension to new culture vessels.
6. Incubate cultures at 37°C.

Subcultivation Ratio: 1:10
Medium Renewal: Every 2 to 3 days

Note: For more information on enzymatic dissociation and subculturing of cell lines consult Chapter 10 in Culture of Animal Cells, a Manual of Basic Technique by R. Ian Freshney, 3rd edition, published by Alan R. Liss, N.Y., 1994.

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