Physical characterization and molecular cloning of the Shope fibroma virus DNA genome

DNA from several independent strains of Shope fibroma virus, a tumorogenic leporipoxvirus of rabbits, was isolated and analyzed by restriction endonuclease digestion and Southern blotting. The restriction profiles indicated a high degree of sequence conservation among the isolates but blotting under standard stringencies revealed no detectable cross homology with a member of the orthopoxvirus group, vaccinia. The genome of the fibroma virus was calculated to be in excess of 160 kilobases and shown to possess two features analogous to the orthopoxvirus group: (1) the terminal restriction fragments possess covalently closed hairpin structures; and (2) the terminal sequences are present as inverted repeats of greater than 10 kilobases. The terminal 3.6 kilobase BamHI restriction fragment was cloned in pBR322 after removal of the hairpin structure with mung bean single strand-specific endonuclease and addition of BamHI linkers. SFV sequences within this terminal region were shown, using 32P SFV cloned terminal probe, to have none of the sequence heterogeneity characteristic of vaccinia DNA termini. The remaining 20 internal SFV BamHI restriction fragments were propagated in bacterial plasmids either as intact fragments, or after secondary digestion with HindIII, and together constitute the complete cloned SFV sequence library.