In the cottontail rabbit papillomavirus (CRPV)-rabbit system, recombinant CRPV
DNA can induce
papillomas. This investigation was undertaken to evaluate whether the E5 open reading frame (ORF) of CRPV is required for
papilloma formation. The CRPV genome we utilized, CRPV-WA, was sequenced in the E5 region and was found to contain one deletion, two insertions, and one transition mutation compared with CRPV-KS, the CRPV genome that has been fully sequenced. Despite these differences, an intact E5 ORF is preserved, supporting the notion that this gene may serve a
biological function. One frameshift and two in-frame mutations were constructed in the small region of the 5' end of the E5 ORF that follows the E2 stop
codon and precedes the L2 ORF. Several hundred rabbit skin sites were inoculated with each
DNA preparation with a jet injector to test the ability of three
CRPV E5 mutant DNAs to induce
papillomas. In vivo results showed that each of the mutants induced
papillomas, and biochemical analysis demonstrated that the E5 mutations present in
DNA inocula were retained in the
papillomas. The frequency of
papilloma formation, however, was generally lower with each of the
CRPV E5 mutants than with wild-type CRPV
DNA, particularly so for the E5 frameshift mutant, suggesting that although the recognized E5 ORF is not required in domestic rabbits for the induction of
papillomas by CRPV
DNA, it may facilitate their formation.