Genetic map of the circular CRPV genome. E6, SE6, E7, E2 and L2 are coded from the open reading frame 1, E8, E4, E5 and L1 are coded from the open reading frame 2 and E1 is from the open reading frame 3. The CRPV genome used for DNA challenge and mutant generation is cloned in PUC19 at single enzyme site in E5 (SalI 4572). To standardized the results, all the mutants were based on Hershey progressive CRPV strain reported in our previous studies. Every mutation was confirmed by DNA sequence analysis.