The distribution of the frequencies of BoLA-DRB3 gene alleles in the Iranian cattle breed Sistani was studied by the PCR-RFLP (“hemi-nested”) assay using restriction endonucleases Rsa I, Hae III and Bst YI. In the examined cattle breed (65 animals) 32 alleles have been identified one of which being described for the first time (6.15% frequency). The nucleotide sequence of the polymorphic region of exon 2 of this allele has been determined and submitted in the GenBank database under accession number DQ486519. The submitted sequence has maximum homology (92%) with the previously described sequence DRB3 -mRNA from Bos indicus (AccN X79346) and differs from it by 24 nucleotide substitutions which result in 16 amino acid substitutions. The peptide (on the basis of the reconstructed amino acid sequence) has 89% identity to the sequence encoded by the BIDRBF 188 locus ( Bos indicus ). The results obtained permit the sequence described by us to be considered as a new allele of the BoLA-DRB3 gene ( DRB3.2 * X ). The total frequency of the main six alleles ( DRB3.2*8, *10, *11 , *20 , *34 and *X ) occurring with a frequency of over 5% is about 60% in Iranian Sistani cattle. Fifteen alleles have <1% frequency. The highest frequency was observed for DRB3.2 * 8 allele (21.54%) like in other previously described breeds of Bos indicus (up to 23.07%). The Iranian breed Sistani has a high level of similarity by the spectrum of BoLA-DRB3 alleles and their frequencies to other Bos indicus breeds and significantly differs by these criteria from the Bos Taurus breeds. The Iranian Sistani herd under study includes alleles associated with to resistance to leukemia ( DRB3.2 * 11 and *23 ) and to different forms of mastitis ( DRB3.2 * 2 , *7 , *11 , *23 and *24 ) although their frequencies are low (from 0.77 to 5.37%). On the whole, a high level of diversity of BoLA-DRB3 gene alleles and the availability of alleles associated with resistance to different diseases makes this breed of interest for breeding practice.

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