Glycoproteins of avian tumor virus recombinants: evidence for intragenic crossing-over

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Abstract
The envelope glycoproteins of several avian tumor virus recombinants selected for the host range of a leukosis virus and the transforming function of a sarcoma virus were compared with each other and with those of their parents. It was found that the glycoproteins of different recombinant viruses, derived from the same parents, differed in their electrophoretic mobilities measured in polyacrylmide gels. The glycoproteins that had lower electrophoretic mobilities had higher precentages of carbohydrate. The carbohydrate of viral glycoproteins was estimated to range between 8 and 18% from their buoyant densities in CsCl, using known glycoproteins as standards. After exhaustive Pronase digestion, the carbohydrate was recovered from viral glycoproteins as a mixture of glycopeptides with molecular weights ranging from 2,500 to 5,000. It was estimated that distinct viral glycoproteins contained between two and five such oligosaccharide chains and that the glycoproteins of different recombinants expressing the same host range marker may differ in the number of oligosaccharide chains and consequently also in their polypeptide structure. Those with lower electrophoretic mobility contain more oligosaccharide chains per molecule than those with higher electrophoretic mobilities. It is suggested that not oligosaccharide chains define the viral host range.