A rabbit class I major histocompatibility complex gene with a T cell-specific expression pattern.

The class I gene family of the rabbit consists of 8 to 12 members and includes a gene that is transcribed only in T cells and in lymphoid tissues containing T cells. A cDNA clone, pR27, was isolated from a cDNA library constructed using mRNA from the T cell line RL-5. The pR27 insert was 1.9 kb long and included sequences that correspond to class I exons 2, 3, and 4 encoding external domains. Intron 4 sequence was found downstream followed by an unusually long 3' region which contained a sequence highly repeated in the rabbit genome. Although the pR27 exons encode structures typical of class I antigens, structural comparisons show no close relationship to other rabbit class I genes in the 3' regions, and no relationship to the 3' region of any murine gene including those encoded in the T1a region. By contrast, similarity of the 3' sequence has been found with human genes of the HLA-A type both by sequence comparison and by DNA hybridization studies. Southern blot analyses with a specific probe from this clone indicated that the gene encoding pR27 is present as a single copy in all rabbit DNA samples examined. Northern blot analysis and S1 nuclease mapping studies revealed that transcripts corresponding to pR27 are present in virally transformed T cell lines, thymus, and, to a lesser extent, in spleen and appendix but not in nonlymphoid tissue. The sizes of the detected transcripts (2.8 and 3.9 kb) were larger than that normally observed for a class I gene.