Genomic changes associated with antigenic variation of visna virus durig persistent infection

Visna virus undergoes antigenic change during persistent infection of sheep. Antigenic variants of visna virus were compared by using the genomic RNA and analyzing the large RNase T1-resistant oligonucleotides. Mutants isolated from a persistently infected sheep contained a small number of changes in their oligonucleotide patterns when compared with parental virus. To determine whether the changes in the nucleotide structure were clustered in one region of the genome, we determined the order of the oligonucleotides of the parental and mutant RNAs along the genome with respect to the 3' polyadenylylated end. All but one difference between the parental strain and the antigenic mutant used for mapping were located within 2 kilobases from the 3' terminus. Nucleotide sequence analyses showed that several of the oligonucleotides that differed in the parental and mutant RNAs could be accounted for by single base changes.