Exon-intron organization of TRGC genes in sheep.

A series of genomic clones derived from a sheep library were used to determine the germline configuration and the exon-intron organization of TRGC2, TRGC3, and TRGC4 genes. Based on the outcomes of molecular analysis, we compared and aligned the genomic sequences with the known complete cDNA sequences of sheep and deduced the exon-intron organization of TRGC genes in this ruminant animal, EX1, corresponding to the disulfide-linked constant domain, and EX3, corresponding to the transmembrane and cytoplasmatic domains, are similar in length in all genes. Conversely, the hinge-encoding EX2A, EX2B, and EX2C exons differ in number and length between genes, and EX2A contains the TTKPP motif irrespective of whether it occurs in single or triplicate form. The molecular data also indicate that at least one additional gene is present in sheep. Phylogenetic analysis grouped the ruminant TRGC genes in two clusters that could have emerged from two ancestral forms that underwent a series of duplications giving rise to the new sequences that were selected and then fixed in the ruminant lineages. A correlation between the cluster distribution in the phylogenetic tree of TRGC genes and their expression during fetal development is discussed.