Abstract
A quantitative focus test was established in mouse embryo fibroblast cultures for the L virus resident in an 8-azaguanine resistant subline (A9) of L cells. The titers obtained were 100-fold higher in N-type than in B-type cells indicating that the L virus is N-tropic. The replication of viruses produced by two Moloney lymphoma sublines (Y and Yr), our L cell (A9) derivative (L), and their hybrid cells (YL and YrL) was studied in BALB 3T3 cells during a six day period. The Y, Yr and YrL viruses were detectable by the XC plaque test, and the L and YL viruses by focus formation. Upon passage in BALB 3T3 cells the original characteristics of these viruses in these two assay systems were retained. The outcome of infection on mouse embryo fibroblasts was similar. The viruses produced by the hybrid cells were found to be different from the viruses resident in each parental cell entering the hybrids.
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