4, Supporting Information Fig. 4 and Table 1). In the TCRGV2-TCRGJ2-2 cDNA clones nine tandem mutations are also present. Since the mRNA sample was prepared from the spleen tissue of a single animal, the sequence diversity observed cannot be explained by allelic variations, nor can it be due to PCR errors because a high-fidelity polymerase was used. The rare occurrence of changes in C region sequences, the absence of changes in nine of the V domain sequences, and the presence see more of the

same mutation in different clones confirms the high fidelity of the polymerase used. The changes observed consisted of 213 nucleotides substitutions, with an overall frequency of 0.008 per base pair (Table 1), much higher than that of a nonrelevant gene (EEF1A1) [14]. The average mutation rate does not depend on the number of PCR cycles,

given that 19 of 22 TCRGV1-TCRGJ1-1 cDNA clones were obtained by half the number of PCR cycles with respect to the TCRGV2-TCRGJ2-2 clones. To exclude the presence of large germline TCRGV gene subfamilies, Southern blotting and quantitative real-time PCR were performed (Supporting Information Fig. 5A–C). Both assays confirmed the TCRG locus arrangement and the sequencing data, i.e. the TCRGV1 and TCRGV2 subgroup is represented by a single gene per haploid CH5424802 genome. Genealogy clonal trees of mutants TCRGV2 sequences within a single rearrangement (Fig. 4) are presented in Fig. 5. Thus, these data demonstrate that somatic mutation occurs in both the dromedary TCRGV and TCRDV region [14], as well as in the sandbar shark TCRGV [13]. The TCR γ chain mutations do not show any bias for transition/transversion changes (Supporting Information Table 2A and B). The target bases are slightly biased toward G and C bases and (A/G/T)G(C/T)(A/T) motif (or DGYW) or its reverse complement (A/T)(A/G)C(C/T/A) (or WRCH), as has been PJ34 HCl shown for IG genes [11, 23]. We were not able to observe a targeting of mutations to

CDR rather than to framework region (FR) (Table 2). The IG mutations from mammals are conventionally evaluated by comparing replacement and synonymous substitutions (R/S ratios) in CDR and FR regions. The ratio in dromedary TCR V domains is higher for CDR than for FR (Table 2), suggesting either selection toward amino acid (AA) changes in CDR or against AA changes in FR. Structural models of the V domains obtained by joining AA sequences of V and J germline TCRGV1-J1-1 (VG1), TCRGV2-J2-2 (VG2), and TCRDV4-TCRDJ4 (VD4) [14] and of VG1/VD4, VG2/VD4 Fv were computed adopting a comparative modeling procedure. Templates were the counterpart γδ subunits of the human γδ T-cell receptor (PDB code: 3 omz) [24, 25]. VG1 and VG2 share a sequence identity of only 29%. However, their 3D structure is highly similar (with a root mean square deviation (RMSD) of 0.69 Å, calculated on the backbone) and they similarly interact with the computed VD4.