Conservation and variation in orf virus genomes

Area of Science:

• Virology
• Molecular Biology
• Genomics

Background:

• Orf virus (ORFV) is an important parapoxvirus affecting livestock.
• Understanding ORFV genome structure and variability is crucial for studying its evolution and pathogenesis.

Purpose of the Study:

• To analyze the genome structure of different orf virus strains.
• To identify regions of conservation and variability within the viral genome.
• To investigate the potential role of variable regions in viral evolution.

Main Methods:

• Restriction endonuclease digestion (EcoRI, HindIII, BamHI, KpnI) of orf virus genomes.
• Deduction of cleavage site maps.
• DNA hybridization studies using cloned viral fragments.
• Restriction endonuclease analysis of cloned DNA fragments.

Main Results:

• Conserved restriction sites were observed in the right half of the genome, while the left half showed more variability.
• Variations in inverted terminal repetitions and a deletion in a subterminal fragment were noted.
• A 20-kbp region approximately 12 kbp from the left end exhibited high cleavage site variability.
• A cloned fragment from this variable region of strain NZ2 did not hybridize with DNA from other strains, indicating significant nonhomology (at least 2.75 kbp).

Conclusions:

• The orf virus genome possesses both conserved and highly variable regions.
• The identified internal variable region shows substantial genetic divergence between strains.
• This internal variable region is a potential site for the integration of foreign genetic material, contributing to viral adaptability.