The generation of a diverse repetoire of antigen binding is the primary function of lymphoid cells. The VDJ recombination activity is the enzyme system which catalyzes this gene segment assembly process. Yet little is known of how this enzyme system mediates the recombination or how it is regulated. A deeper understanding of this key enzyme system is important to basic immunology. This central enzyme system also relates to congenital immunodeficiencies in which the enzyme system may be defective; chromosomal translocations, which in a major fraction of leukemias and lymphomas appear to be catalyzed by the VDJ recombination activity; and biases in the way the VDJ recombination activity selects gene segments, an aspect that may be relevant to autoimmunity. In this project, a set of studies are proposed that attempt to define aspects of how the VDJ recombination activity functions. How does the VDJ recombination activity locate the signal sequences? One hypothesis that will be rigorously tested here is whether the enzyme system tracks along the DNA from site to site. If intermolecular recombination can occur between VDJ recombination signals, then this rules out such a tracking mechanism. Intermolecular recombination is of particular relevance to chromosomal translocation mechanisms. In addition, what is the effect of alterations in the signal and coding sequences on the efficiency of the VDJ recombination reaction and the extent of diversity generated? Are transcription or replication required for VDJ recombination to occur as some research has suggested? The murine scid defect provides a potential model for human congenital immunodeficiency states. Our previous work has determined that the two halves of the VDJ recombination reaction are uncoupled in scid and that the physiologically important portion of the reaction, coding joint formation, fails. In this proposal, a deeper understanding of why the coding joint formation fails is pursued. Is the recombination activity covalently linked to the coding end termini in the aborted scid VDJ recombination reaction? Finally, identification and purification of the gene affected in severe combined immune deficiency will permit one component of this enzyme system to be studied at the genetic level.
