Exon-intron organization of TRGC genes in sheep

A series of genomic clones derived from a sheep library were used to determ ine the germline configuration and the exon-intron organization of TRGC2, T RGC3, and TRGC4 genes. Based on the outcomes of molecular analysis, we comp ared and aligned the genomic sequences with the known complete cDNA sequenc es 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, ar e similar in length in all genes. Conversely, the hinge-encoding EX2A, EX2B , and EX2C exons differ in number and length between genes, and EX2A contai ns the TTKPP motif irrespective of whether it occurs in single or triplicat e 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 under went a series of duplications giving rise to the new sequences that were se lected and then fixed in the ruminant lineages. A correlation between the c luster distribution in the phylogenetic tree of TRGC genes and their expres sion during fetal development is discussed.