Characterisation of a cluster of TRIM-B30.2 genes in the chicken MHC B locus.

We have identified and characterised a cluster of six TRIM-B30.2 genes flanking the chicken BF/BL region of the B complex. The TRIM-B30.2 proteins are a subgroup of the TRIM protein family containing the tripartite motif (TRIM), consisting of a RING domain, a B-box and a coiled coil region, and a B30.2-like domain. In humans, a cluster of seven TRIM-B30.2 genes has been characterised within the MHC on Chromosome 6p21.33. Among the six chicken TRIM-B30.2 genes two are orthologous to those of the human MHC, and two (TRIM41 and TRIM7) are orthologous to human genes located on Chromosome 5. In humans, these last two genes are adjacent to GNB2L1, a guanine nucleotide-binding protein gene, the ortholog of the chicken c12.3 gene situated in the vicinity of the TRIM-B30.2 genes. This suggests that breakpoints specific to mammals have occurred and led to the remodelling of their MHC structure. In terms of structure, like their mammalian counterparts, each chicken gene consists of five coding exons; exon 1 encodes the RING domain and the B-box, exons 2, 3 and 4 form the coiled-coil region, and the last exon represents the B30.2-like domain. Phylogenetic analysis led us to assume that this extended BF/BL region may be similar to the human extended class I region, because it contains a cluster of BG genes sharing an Ig-V like domain with the BTN genes (Henry et al. 1997a) and six TRIM-B30.2 genes containing the B30.2-like domain, shared with the TRIM-B30.2 members and the BTN genes.