Sequencing and genetic analysis of a bovine DQB cDNA clone

Abstract

Summary. A BoLA‐DQB cDNA clone (BoLA‐DQß‐1) was isolated by screening a bovine lymphoblastoid cDNA library with a HLA‐DQB genomic clone. The DNA and predicted protein sequences were compared to class II sequences from cattle and other species. BoLA‐DQß‐1 has 92.0% similarity to the coding regions of two previously sequenced BoLA‐DQB genomic clones and 69.6% similarity to a BoLA‐DRß pseudogene. However, the first domain encoded by BoLA‐DQß‐1 has 94 amino acids; one more than the predicted size of the products encoded by two previously sequenced bovine DQB genes (BoDQß‐Q1 and BoDQß‐Y1). Comparing all coding regions, BoLA‐DQß‐1 has greater nucleotide similarity to HLA‐DQB sequences than to I‐Aß, HLA‐DRB and 1‐Eß sequences. Like the HLA‐DQB gene product, the cytoplasmic domain of the predicted protein encoded by BoLA‐DQß‐1 is eight amino acids shorter than that of I‐Aß, HLA‐DRB and I‐Eß molecules. Six clone‐specific amino acid substitutions were identified in the ß1 domain of BoLA‐DQß‐1, including an unusual cysteine residue at position 13 which is believed to be positioned on a ß‐strand and face into the antigen recognition site. Southern blot analysis of Pvu II‐digested genomic DNA from a paternal half‐sibling famil (sire, and six dam‐offspring pairs) using BoLA‐DQß‐1 as a probe, revealed five allelic Pvu II RFLP patterns, including two patterns not previously described, that cosegregated with serologically‐defined BoLA‐A (class I) alleles. The evolution, polymorphism and function of a transcriptionally active BoLA‐DQB gene can now be readily studied using this DQB cDNA clone as a source of allele and locus‐specific oligonucleotide primers.