A BAC clone-based physical map of ovine major histocompatibility complex

An ovine bacterial artificial chromosome (BAC) library containing 190,000 BAC clones was constructed and subsequently screened to construct a BAC-based physical map for the ovine major histocompatibility complex (MHC). Two hundred thirty-three BAC clones were selected by 84 overgo probes designed on human, mouse, and swine MHC sequence homologies. Ninety-four clones were ordered by DNA fingerprinting to form contigs I, II, and III that correspond to ovine MHC class I–class III, class IIa, and class IIb. The minimum tiling paths of contigs I, II, and III are 15, 4, and 4 BAC clones, spanning approximately 1900, 400, and 300 kb, respectively. The order and orientation of most BAC clones in each contig were confirmed by BAC-end sequencing. An open gap exists between class IIa and class III. This work helps to provide a foundation for detailed study of ovine MHC genes and of evolution of MHCs in mammals.