Loss of Proviral DNA Sequences in a Revertant of Kirsten Sarcoma Virus-transformed Murine Fibroblasts

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Abstract
A previously described revertant [murine fibroblast] cell line (K-BALB SR 1212), derived as a single cell clone from a clonal line of murine fibroblasts (K-BALB) transformed by a nonproductive infection with the Kirsten strain of murine sarcoma virus [Ki-MSV], has normal morphology and growth kinetics and, unlike the transformed parent cell line, lacks a sarcoma virus that can be rescued. This reversion correlates with low to undetectable levels of expression of cellular Ki-MSV-specific RNA and a reduction of proviral sequences in the cell DNA to a level equivalent to that found in the uninfected BALB cells with a normal phenotype. The data indicate that phenotypic reversion occurred as a consequence of the loss of part or all of the sarcoma provirus, either by chromosomal rearrangement or provirus excision.