PERSISTENCE OF THE SV40 EARLY REGION WITHOUT EXPRESSION IN PERMISSIVESIMIAN CELLS

SV40 containing recombinant vectors were introduced into permissive si mian, non-permissive rodent and semi-permissive human cell lines, and assayed for transformation. All mouse and human cell clones expressed T-antigen (T-Ag) and were morphologically transformed when they contai ned only the wt T-Ag gene (E-SV40) or the entire wt viral genome with an interrupted late region. However, of 63 simian clones with these re combinant vectors, none became morphologically transformed and T-Ag co ntaining cells were rare or absent. Nearly all simian cell lines made either no detectable early SV40 RNA or only small amounts of viral RNA but contained viral DNA restriction fragments similar to those in the original recombinant vectors. Functional T-Ag genes were recoverable from several cell clones and used to regenerate infectious virus. Henc e, T-Ag gene expression had been suppressed. We found two conditions w here T-Ag expression was activated. In a BSC-1 cell line containing E- SV40 DNA, subsequent introduction of a vector with a functional viral late coding region (L-SV40) resulted in the appearance of T-Ag and tra nsformation. These findings suggest that L-SV40 sequences activate or enhance T-Ag expression and that this activation requires a functional VpI gene. We found also, that vectors with E-SV40 DNA from the bipart ite variant EL-SV40 consistently transformed simian CV-1 cells. Transf ormation was shown to be effected by the multiple alterations present in the regulatory region of this variant.