Genomic sequence and organization of rabbit Tcrb constant region genes

We previously reported that some rabbits have three different copies of T-cell receptor b (Tcrb) constant region genes unlike man, mice, and rats who generally have two copies. Two of theseCs genes were found on an ≈ 14 kilobase (kb) and one on an ≈ 6 kbEco RI fragment. The gene on the 6 kb fragment is of s2 type. A previously described portion of the 14 kb fragment appeared to have sequences characteristic ofCs1. We have now shown that the 6 kb fragment is adjacent to and 3′ of the 14 kb fragment. Furthermore, the second linked sequence ofCs gene present on the 14 kb fragment resembles to a large extent theCs2 gene present on the 6 kb fragment. Moreover, this secondCs gene has a 5′ cluster ofJs sequences resemblingJs2 of other species. However, exon 4 and the 3′ unranslated region (3′UT) are of the s1 type. Mapping studies using southern analyses of both genomic DNA and the 14 kb clone have identified another cluster ofJs2 sequences 5′ of the third tandemCs2 gene present on the 6 kbEco RI fragment. Thus, the second gene on the 14 kb fragment appears to be a chimeric genomicTcrb gene that may have arisen by an unequal crossing-over event analogous to that which may have deletedCs1,Ds2, andJs2 in NZW mice.