The major goal of this research is to determine the role of Endo-SR (Endonuclease implicated in Switch/Somatic Recombination) in B-cell specific gene recombination or other DNA processing events. Endo-SR was initially discovered through its ability to preferentially cleave immunoglobulin (lg) switch repeat sequences commonly found at lg isotype-switch recombination breakpoints. This enzyme has been purified to homogeneity from bovine spleen nuclear extracts and partial peptide sequence information from the purified protein has been obtained. Sequence homology searches performed with these peptides revealed significant similarities to the predicted amino acid sequences of hypothetical human and C. elegans proteins identified by the Human and C. elegans Genome Projects. The identified human protein has recently been reported to encode an endonuclease implicated in nuclear DNA degradation induced during programmed cell death. Preliminary evidence indicates that the C. elegans protein also encodes an endonuclease implicated in apoptotic nuclear DNA degradation. The recent isolation of the Endo-SR gene should greatly facilitate a rigorous analysis of the in vivo regulation and function of this enzyme. As part of this analysis, Endo-SR mutant cell lines will be generated by targeted gene disruption. Assays conducted with these Endo-SR deficient cells should allow definitively conclusions as to whether or not this nuclease activity is required for switch recombination and/or apoptosis. This research should greatly enhance current understanding of the molecular and biochemical roles of an enzyme that has been implicated in both a lymphocyte-specific DNA recombination process and a general DNA degradation process induced by apoptosis.
