Biochemical evidence of recombination within the unsegmented RNA genome of aphthovirus

Four different pairs of temperature-sensitive mutants, derived from the same strain of aphthovirus, were crossed by using an infectious center recombination test. Each parental mutant carried an unselected marker affecting the isoelectric point of a virus-coded polypeptide; progeny of the crosses, able to grow at the nonpermissive temperature, were screened for these unselected markers. Polypeptide charge was shown to be a stable, inheritable character, and three of the four crosses yielded genetic recombinants that possessed the polypeptide marker from both parents. Peptide fingerprinting and high-resolution isoelectric focusing of the polypeptides ruled out the explantation that these viruses were generated by mutation.