3 LYMPHOID-SPECIFIC FACTORS ACCOUNT FOR ALL JUNCTIONAL DIVERSITY CHARACTERISTIC OF SOMATIC ASSEMBLY OF T-CELL RECEPTOR AND IMMUNOGLOBULIN GENES

The somatic diversity immunoglobulin and T-cell receptor diversity is largely provided by the junctional variation created during site-speci fic rearrangement of separately encoded gene segments. Using a transie nt transfection assay, we demonstrate that the recombination activatin g genes Rag1 and Rag2 direct site-specific rearrangement on an artific ial substrate in poorly differentiated as well as in differentiated no nlymphoid cell lines. In addition to a high frequency of precise recom bination events, coding joints show deletions and more rarely P-nucleo tide insertions, reminiscent of immunoglobulin and T-cell receptor jun ctions found in fetal tissues. N-region insertions, which are characte ristic of adult junctional diversity, are obtained at high frequency u pon transfection of a terminal deoxynucleotidyltransferase expression vector together with Rag1 and Rag2. These results show that only three lymphoid-specific factors are needed to generate all types of junctio nal diversity observed during lymphoid development.