1887

Abstract

, a major pathogen of poultry, contains a single expressed, full-length gene encoding its haemagglutinin, and a large number of pseudogenes that can be recruited by multiple site-specific recombination events to generate chimaeric variants of the expressed gene. The position and distribution of the pseudogene regions, and their relationship with the expressed gene, have not been investigated. To determine the relationship between these regions, a physical map of the genome was constructed using the restriction endonucleases I, I, WI, I and I and radiolabelled probes for , and . A cloned fragment encoding the unique portion of the expressed gene and two PCR products containing conserved regions of the ORF 3 and ORF 6 pseudogenes were used to locate the regions containing these genes on the map. The chromosome of was found to be 890·4 kb and the two rRNA operons were in the same orientation. Both the expressed gene and the pseudogenes were confined to the same 114 kb region of the chromosome. These findings indicate that, unlike , in which the genes are located in several loci around the chromosome and in which antigenic variation is generated by alternating transcription of over 40 translationally competent genes, has all of the sequences clustered together, suggesting that close proximity is needed to facilitate the site-specific recombinations used to generate diversity in the expressed gene.

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2005-03-01
2019-10-14
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