Molecular investigations on 18 naturally occurring sarcoid tumors removed from donkeys identified papillomaviral DNA homologous to bovine papillomavirus (BPV)-2 DNA under stringent conditions, in all the samples. Restriction endonuclease analysis of 15 of the tumours demonstrated papillomaviral DNA similar to BPV-1 and BPV-2. The type of DNA was not specific to either the site or the type of lesion. The analysis of the nucleotide base sequence of a cloned papillomaviral element from a sarcoid showed that the isolate was 96 and 98 per cent homologous to BPV-1 in the L1 and E5 open reading frames, respectively. It was concluded that the disease in the donkey is similar to that in the horse and that the E5 open reading frame may be involved in oncogenesis in the sarcoid.
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