Replication efficiency of JCV and SV40 Pt mutants. (A) SVG-A cells were transfected with either JCV Mad-1 WT or the Pt mutant genome. Low molecular-weight DNA was isolated at the time points indicated, digested with BamH I and Dpn I enzymes, resolved on a 0.8% agarose gel, and analyzed by Southern blotting. In lane 1, JCV Mad-1 WT genome (2 ng) digested with BamH I was loaded as a positive control (+ Cont.). (B) CV-1 cells were transfected with either SV40(776) WT or its Pt mutant genome and the replication efficiency of both genomes was assessed by Southern blotting as described for panel A. Replication studies with WT and the Pt mutants for both JCV and SV40 genomes were repeated more than three times and a representative data is shown here. The input DNA (transfected), which is digested by Dpn I is indicated by the brackets. In lane 1, SV40(776) genome (2 ng) digested with BamH I was loaded as a positive control (+ Cont.).