ALLELIC VARIATION OF OVINE MHC CLASS-II DQA1 AND DQA2 GENES

In the present study we characterize allelic Variation of polymorphic OLA-DQA1 and OLA-DQA2 genes in sheep. To achieve this, PCR primers wer e designed to independently amplify the second exons of OLA-DQA1 and O LA-DQA2 genes. Single strand conformation polymorphism (SSCP) gel anal yses reveals that there are at least 12 distinct OLA-DQA2 sequences, 1 0 of which have been characterized by sequencing. Six distinct OLA-DQA 1 alleles have been sequenced in sheep and we can detect at least seve n DQA1 alleles, including a null allele, by SSCP analysis. The second exon of the OLA-DQA2 gene is more polymorphic than the equivalent regi on of the OLA-DQA1 gene. Thirty-two per cent of nucleotide and 49% of amino acid sites showed variation at the DQA2 locus, compared to 20% o f nucleotide and 33% of amino acid sites for DQA1. Phylogenetic analys is of DQA sequences from a number of species show that sheep DQA1 sequ ences group together and are more similar to bovine DaA1 sequences tha n to sheep DQA2 alleles. The majority of OLA-DQA2 sequences are on the same main branch of the phylogenetic tree as bovine DQA2 sequences. H owever, three sheep DQA2 sequences have a tendency to group with putat ive bovine DQA3 sequences rather than to other ovine DQA2 alleles. A v ariety of SSCP gel conditions were Med in order to develop a typing sy stem for the OLA-DQA2 gene. We describe a set of PCR and SSCP conditio ns which distinguish between all known OLA-DQA2 alleles.