Characterization of tissue culture-induced heterogeneity in DNAs of independent isolates of JC virus

After several serial passages at low multiplicities of infection in primary human foetal glial cells at 37 °C, the DNA of prototype (MAD-I) JC virus and that of MAD-2 and MAD-3 are typically heterogeneous in size, but DNAs of MAD-4 and MAD-6 are relatively homogeneous. A similar dichotomy was observed in the DNAs of six isolates propagated more recently in glial cultures at 39 °C under similar conditions of brief passage in vitro at low multiplicities of infection: the DNAs of two (MAD-9 and-10) were heterogeneous, but the DNAs of four others (MAD-8,-11,-12 and-14) were homogeneous. Therefore, the propensity of the viral genome to sustain deletions was n intrinsic property of each isolate. However, actual induction and maintenance of the presumably defective DNAs was influenced by the relative proportions of permissive spongioblasts and semi-permissive astrocytes in the glial cultures and by the multi-plicity of infection. Deletions in MAD-1 DNA were confined to the presumptive early region and spanned the BamHI cleavage site (map position 0.505). The heterogeneity was more complex in the DNAs of MAD-2 and MAD-3, but again most of the deletions, which ranged up to 12~o f full-length DNA, spanned the BamHI site. We propose that the differential susceptibility to deletion among isolates is a consequence of natural genetic variation in JC virus