Rapid Screening Assay for Revertants derived from MSV-transformed Cells

MURINE sarcoma virus (MSV)-transformed 3T3FL cells (S + L − cells 1 ) produced spontaneously and at variable rates flat variants (revertants) from which MSV could no longer be rescued by superinfection with murine leukaemia virus (MuLV) 2,3 . During the course of investigation of reversion frequency in S + L − cells, we have been able to detect revertants by a rapid screening assay technique instead of using the more cumbersome cloning procedure in microtitre wells as previously described 2,3 . The S + L − cell line 3197 1–3 was composed of hyper-refractile, loosely attached cells and did not form a compact cell monolayer. Infection of this cell line with MuLV changed the cellular morphology to a slightly more rounded cell type, and increased the tendency of cells to detach readily from the surface of the container. When rescue-negative revertants derived from S + L − cells were infected with MuLV there was no observable change in cellular morphology. These characteristics can be used as the basis for a rapid screening assay technique for revertants from S + L − cells, the details of which are described here.